Communication apparatus and retransmission control method

ABSTRACT

Provided is a terminal device that is capable of improving the characteristics of a response signal having poor transmission characteristics when ARQ is utilized in communication using an uplink unit band and a plurality of downlink unit bands associated with the uplink unit band. At the time of channel selection, a control unit selects a resource used in sending a response signal from among specific PUCCH resources notified in advance from a base station and PUCCH resources mapped to a CCE, and controls the transmission of the response signal. A response signal generating unit supports implicit signaling with respect to any given response signal, and at the same time as supporting LTE fallback from 2CC, uses a mapping method that, between bits, smooths the number of PUCCH resources that can determine ACK/NACK simply by determining the PUCCH resource regarding which the response signal had notified.

BACKGROUND Technical Field

The claimed invention relates to a terminal apparatus and aretransmission control method.

Description of the Related Art

3GPP LTE employs Orthogonal Frequency Division Multiple Access (OFDMA)as a downlink communication scheme. In radio communication systems towhich 3GPP LTE is applied, base stations transmit synchronizationsignals (i.e., Synchronization Channel: SCH) and broadcast signals(i.e., Broadcast Channel: BCH) using predetermined communicationresources. Meanwhile, each terminal finds an SCH first and therebyensures synchronization with a base station. Subsequently, the terminalreads BCH information to acquire base station-specific parameters (see,Non-Patent Literatures (hereinafter, abbreviated as NPL) 1, 2 and 3).

In addition, upon completion of the acquisition of the basestation-specific parameters, each terminal sends a connection request tothe base station to thereby establish a communication link with the basestation. The base station transmits control information via PhysicalDownlink Control CHannel (PDCCH) as appropriate to the terminal withwhich a communication link has been established.

The terminal performs “blind-determination” on each of a plurality ofpieces of control information included in the received PDCCH signals(i.e., Downlink (DL) Assignment Control Information: also referred to asDownlink Control Information (DCI)). To put it more specifically, eachpiece of the control information includes a Cyclic Redundancy Check(CRC) part and the base station masks this CRC part using the terminalID of the transmission target terminal. Accordingly, until the terminaldemasks the CRC part of the received piece of control information withits own terminal ID, the terminal cannot determine whether or not thepiece of control information is intended for the terminal. In thisblind-determination, if the result of demasking the CRC part indicatesthat the CRC operation is OK, the piece of control information isdetermined as being intended for the terminal.

Moreover, in 3GPP LTE, Automatic Repeat Request (ARQ) is applied todownlink data to terminals from a base station. To put it morespecifically, each terminal feeds back response signals indicating theresult of error detection on the downlink data to the base station. Eachterminal performs a CRC on the downlink data and feeds backAcknowledgment (ACK) when CRC=OK (no error) or Negative Acknowledgment(NACK) when CRC=Not OK (error) to the base station as response signals.An uplink control channel such as Physical Uplink Control Channel(PUCCH) is used to feed back the response signals (i.e., ACK/NACKsignals (hereinafter, may be referred to as “A/N,” simply)).

The control information to be transmitted from a base station hereinincludes resource assignment information including information onresources assigned to the terminal by the base station. As describedabove, PDCCH is used to transmit this control information. The PDCCHincludes one or more L1/L2 control channels (L1/L2 CCH). Each L1/L2 CCHconsists of one or more Control Channel Elements (CCE). To put it morespecifically, a CCE is the basic unit used to map the controlinformation to PDCCH. Moreover, when a single L1/L2 CCH consists of aplurality of CCEs (2, 4 or 8), a plurality of contiguous CCEs startingfrom a CCE having an even index are assigned to the L1/L2 CCH. The basestation assigns the L1/L2 CCH to the resource assignment target terminalin accordance with the number of CCEs required for reporting the controlinformation to the resource assignment target terminal. The base stationmaps the control information to physical resources corresponding to theCCEs of the L1/L2 CCH and transmits the mapped control information.

In addition, CCEs are associated with component resources of PUCCH(hereinafter, may be referred to as “PUCCH resource”) in a one-to-onecorrespondence. Accordingly, a terminal that has received an L1/L2 CCHidentifies the component resources of PUCCH that correspond to the CCEsforming the L1/L2 CCH and transmits response signals to the base stationusing the identified resources. However, when the L1/L2 CCH occupies aplurality of contiguous CCEs, the terminal transmits the responsesignals to the base station using a PUCCH component resourcecorresponding to a CCE having a smallest index among the plurality ofPUCCH component resources respectively corresponding to the plurality ofCCEs (i.e., PUCCH component resource associated with a CCE having aneven numbered CCE index). In this manner, the downlink communicationresources are efficiently used.

As illustrated in FIG. 1, a plurality of response signals transmittedfrom a plurality of terminals are spread using a Zero Auto-correlation(ZAC) sequence having the characteristic of zero autocorrelation intime-domain, a Walsh sequence and a discrete Fourier transform (DFT)sequence, and are code-multiplexed in a PUCCH. In FIG. 1, (W₀, W₁, W₂,W₃) represent a length-4 Walsh sequence and (F₀, F₁, F₂) represent alength-3 DFT sequence. As illustrated in FIG. 1, ACK or NACK responsesignals are primary-spread over frequency components corresponding to 1SC-FDMA symbol by a ZAC sequence (length-12) in frequency-domain. To putit more specifically, the length-12 ZAC sequence is multiplied by aresponse signal component represented by a complex number. Subsequently,the ZAC sequence serving as the response signals and reference signalsafter the primary-spread is secondary-spread in association with each ofa Walsh sequence (length-4: W₀-W₃ (may be referred to as Walsh CodeSequence)) and a DFT sequence (length-3: F₀-F₂). To put it morespecifically, each component of the signals of length-12 (i.e., responsesignals after primary-spread or ZAC sequence serving as referencesignals (i.e., Reference Signal Sequence) is multiplied by eachcomponent of an orthogonal code sequence (i.e., orthogonal sequence:Walsh sequence or DFT sequence). Moreover, the secondary-spread signalsare transformed into signals of length-12 in the time-domain by inversefast Fourier transform (IFFT). A CP is added to each signal obtained byIFFT processing, and the signals of one slot consisting of seven SC-FDMAsymbols are thus formed.

The response signals from different terminals are spread using ZACsequences each corresponding to a different cyclic shift value (i.e.,index) or orthogonal code sequences each corresponding to a differentsequence number (i.e., orthogonal cover index (OC index)). An orthogonalcode sequence is a combination of a Walsh sequence and a DFT sequence.In addition, an orthogonal code sequence is referred to as a block-wisespreading code in some cases. Thus, base stations can demultiplex thecode-multiplexed plurality of response signals using the related artdespreading and correlation processing (see, NPL 4).

However, it is not necessarily true that each terminal succeeds inreceiving downlink assignment control signals because the terminalperforms blind-determination in each subframe to find downlinkassignment control signals intended for the terminal. When the terminalfails to receive the downlink assignment control signals intended forthe terminal on a certain downlink component carrier, the terminal wouldnot even know whether or not there is downlink data intended for theterminal on the downlink component carrier. Accordingly, when a terminalfails to receive the downlink assignment control signals intended forthe terminal on a certain downlink component carrier, the terminalgenerates no response signals for the downlink data on the downlinkcomponent carrier. This error case is defined as discontinuoustransmission of ACK/NACK signals (DTX of response signals) in the sensethat the terminal transmits no response signals.

In 3GPP LTE systems (may be referred to as “LTE system,” hereinafter),base stations assign resources to uplink data and downlink data,independently. For this reason, in the 3GPP LTE system, terminals (i.e.,terminals compliant with LTE system (hereinafter, referred to as “LTEterminal”)) encounter a situation where the terminals need to transmituplink data and response signals for downlink data simultaneously in theuplink. In this situation, the response signals and uplink data from theterminals are transmitted using time-division multiplexing (TDM). Asdescribed above, the single carrier properties of transmission waveformsof the terminals are maintained by the simultaneous transmission ofresponse signals and uplink data using TDM.

In addition, as illustrated in FIG. 2, the response signals (i.e.,“A/N”) transmitted from each terminal partially occupy the resourcesassigned to uplink data (i.e., Physical Uplink Shared CHannel (PUSCH)resources) (i.e., response signals occupy some SC-FDMA symbols adjacentto SC-FDMA symbols to which reference signals (RS) are mapped) and arethereby transmitted to a base station in time-division multiplexing(TDM). In FIG. 2, however, “subcarriers” in the vertical axis of thedrawing are also termed as “virtual subcarriers” or “time contiguoussignals,” and “time contiguous signals” that are collectively inputtedto a discrete Fourier transform (DFT) circuit in a SC-FDMA transmitterare represented as “subcarriers” for convenience. To put it morespecifically, optional data of the uplink data is punctured due to theresponse signals in the PUSCH resources. Accordingly, the quality ofuplink data (e.g., coding gain) is significantly reduced due to thepunctured bits of the coded uplink data. For this reason, base stationsinstruct the terminals to use a very low coding rate and/or to use verylarge transmission power so as to compensate for the reduced quality ofthe uplink data due to the puncturing.

Meanwhile, the standardization of 3GPP LTE-Advanced for realizing fastercommunications than 3GPP LTE has started. 3GPP LTE-Advanced systems (maybe referred to as “LTE-A system,” hereinafter) follow 3GPP LTE systems(may be referred to as “LTE system,” hereinafter). 3GPP LTE-Advanced isexpected to introduce base stations and terminals capable ofcommunicating with each other using a wideband frequency of 40 MHz orgreater to realize a downlink transmission rate up to 1 Gbps or above.

In the LTE-A system, in order to simultaneously achieve backwardcompatibility with the LTE system and ultra-high-speed communicationsseveral times faster than transmission rates in the LTE system, theLTE-A system band is divided into “component carriers” of 20 MHz orbelow, which is the bandwidth supported by the LTE system. In otherwords, the “component carrier” is defined herein as a band having amaximum width of 20 MHz and as the basic unit of communication band.Moreover, “component carrier” in downlink (hereinafter, referred to as“downlink component carrier”) is defined as a band obtained by dividinga band according to downlink frequency bandwidth information in a BCHbroadcasted from a base station or as a band defined by a distributionwidth when a downlink control channel (PDCCH) is distributed in thefrequency domain. In addition, “component carrier” in uplink(hereinafter, referred to as “uplink component carrier”) may be definedas a band obtained by dividing a band according to uplink frequency bandinformation in a BCH broadcasted from a base station or as the basicunit of a communication band of 20 MHz or below including a PhysicalUplink Shared CHannel (PUSCH) in the vicinity of the center of thebandwidth and PUCCHs for LTE on both ends of the band. In addition, theterm “component carrier” may be also referred to as “cell” in English in3GPP LTE-Advanced.

The LTE-A system supports communications using a band obtained byaggregating several component carriers, so called “carrier aggregation.”In general, throughput requirements for uplink are different fromthroughput requirements for downlink. For this reason, so called“asymmetric carrier aggregation” has been also discussed in the LTE-Asystem. In asymmetric carrier aggregation, the number of componentcarriers configured for any terminal compliant with the LTE-A system(hereinafter, referred to as “LTE-A terminal”) differs between uplinkand downlink. In addition, the LTE-A system supports a configuration inwhich the numbers of component carriers are asymmetric between uplinkand downlink, and the component carriers have different frequencybandwidths.

FIG. 3 is a diagram provided for describing asymmetric carrieraggregation and a control sequence applied to individual terminals. FIG.3 illustrates a case where the bandwidths and numbers of componentcarriers are symmetric between the uplink and downlink of base stations.

As illustrated in FIG. 3B, a configuration in which carrier aggregationis performed using two downlink component carriers and one uplinkcomponent carrier on the left is set for terminal 1, while aconfiguration in which the two downlink component carriers identicalwith those used by terminal 1 are used but uplink component carrier onthe right is used for uplink communications is set for terminal 2.

Referring to terminal 1, an LTE-A base station and an LTE-A terminalincluded in the LTE-A system transmit and receive signals to and fromeach other in accordance with the sequence diagram illustrated in FIG.3A. As illustrated in FIG. 3A, (1) terminal 1 is synchronized with thedownlink component carrier on the left when starting communications withthe base station and reads information on the uplink component carrierpaired with the downlink component carrier on the left from a broadcastsignal called system information block type 2 (SIB2). (2) Using thisuplink component carrier, terminal 1 starts communications with the basestation by transmitting, for example, a connection request to the basestation. (3) Upon determining that a plurality of downlink componentcarriers need to be assigned to the terminal, the base station instructsthe terminal to add a downlink component carrier. However, in this case,the number of uplink component carriers is not increased, and terminal1, which is an individual terminal, starts asymmetric carrieraggregation.

In addition, in the LTE-A system to which carrier aggregation isapplied, a terminal may receive a plurality of pieces of downlink dataon a plurality of downlink component carriers at a time. In LTE-A,studies have been carried out on channel selection (also referred to as“multiplexing”), bundling and a discrete Fourier transform spreadorthogonal frequency division multiplexing (DFT-S-OFDM) format as amethod of transmitting a plurality of response signals for the pluralityof pieces of downlink data. In channel selection, not only symbol pointsused for response signals, but also the resources to which the responsesignals are mapped are varied in accordance with the pattern for resultsof the error detection on the plurality of pieces of downlink data.Compared with channel selection, in bundling, ACK or NACK signalsgenerated according to the results of error detection on the pluralityof pieces of downlink data are bundled (i.e., bundled by calculating alogical AND of the results of error detection on the plurality of piecesof downlink data, provided that ACK=1 and NACK=0), and response signalsare transmitted using one predetermine resource. In transmission usingthe DFT-S-OFDM format, a terminal jointly encodes (i.e., joint coding)the response signals for the plurality of pieces of downlink data andtransmits the coded data using the format (see, NPL 5). For example, aterminal may feed back the response signals (i.e., ACK/NACK) usingchannel selection, bundling or DFT-S-OFDM according to the number ofbits for a pattern for results of error detection. Alternatively, a basestation may previously configure the method of transmitting the responsesignals.

More specifically, channel selection is a technique that varies not onlythe phase points (i.e., constellation points) for the response signalsbut also the resources used for transmission of the response signals(may be referred to as “PUCCH resource,” hereinafter) on the basis ofwhether the results of error detection on the plurality of pieces ofdownlink data received on the plurality of downlink component carriersare each an ACK or NACK as illustrated in FIG. 4. Meanwhile, bundling isa technique that bundles ACK/NACK signals for the plurality of pieces ofdownlink data into a single set of signals and thereby transmits thebundled signals using one predetermined resource (see, NPLs 6 and 7).Hereinafter, the set of the signals formed by bundling ACK/NACK signalsfor a plurality of pieces of downlink data into a single set of signalsmay be referred to as “bundled ACK/NACK signals.”

The following two methods are considered as a possible method oftransmitting response signals in uplink when a terminal receivesdownlink assignment control information via a PDCCH and receivesdownlink data.

One of the methods is to transmit response signals using a PUCCHresource associated in a one-to-one correspondence with a controlchannel element (CCE) occupied by the PDCCH (i.e., implicit signaling)(hereinafter, method 1). More specifically, when DCI intended for aterminal served by a base station is allocated in a PDCCH region, eachPDCCH occupies a resource consisting of one or a plurality of contiguousCCEs. In addition, as the number of CCEs occupied by a PDCCH (i.e., thenumber of aggregated CCEs: CCE aggregation level), one of aggregationlevels 1, 2, 4 and 8 is selected according to the number of informationbits of the assignment control information or a propagation pathcondition of the terminal, for example.

The other method is to previously report a PUCCH resource to eachterminal from a base station (i.e., explicit signaling) (hereinafter,method 2). To put it differently, each terminal transmits responsesignals using the PUCCH resource previously reported by the base stationin method 2.

In addition, as illustrated in FIG. 4, one of the two downlink componentcarriers is paired with one uplink component carrier to be used fortransmission of response signals. The downlink component carrier pairedwith the uplink component carrier to be used for transmission ofresponse signals is called a primary component carrier (PCC) or aprimary cell (PCell). In addition, the downlink component carrier otherthan the primary component carrier is called a secondary componentcarrier (SCC) or a secondary cell (SCell). For example, PCC (or PCell)is the downlink component carrier used to transmit broadcast informationabout the uplink component carrier on which response signals to betransmitted (e.g., system information block type 2 (SIB 2)).

In method 2, PUCCH resources common to a plurality of terminals (e.g.,four PUCCH resources) may be previously reported to the terminals from abase station. For example, terminals may employ a method to select onePUCCH resource to be actually used, on the basis of a transmit powercontrol (TPC) command of two bits included in DCI in SCell. In thiscase, the TPC command is called an ACK/NACK resource indicator (ARI).Such a TPC command allows a certain terminal to use an explicitlysignaled PUCCH resource in a certain frame while allowing anotherterminal to use the same explicitly signaled PUCCH resource in anothersubframe in the case of explicit signaling.

Meanwhile, in channel selection, a PUCCH resource in an uplink componentcarrier associated in a one-to-one correspondence with the top CCE indexof the CCEs occupied by the PDCCH indicating the PDSCH in PCC (PCell)(i.e., PUCCH resource in PUCCH region 1 in FIG. 4) is assigned (implicitsignaling).

Next, a description will be provided regarding ARQ control using channelselection when the asymmetric carrier aggregation described above isapplied to terminals with reference to FIGS. 4 and 5.

In a case where a component carrier group (may be referred to as“component carrier set” in English) consisting of downlink componentcarrier 1 (PCell), downlink component carrier 2 (SCell) and uplinkcomponent carrier 1 is configured for terminal 1 as illustrated in FIG.4, after downlink resource assignment information is transmitted via aPDCCH of each of downlink component carriers 1 and 2, downlink data istransmitted using the resource corresponding to the downlink resourceassignment information.

In channel selection, when terminal 1 succeeds in receiving the downlinkdata on component carrier 1 (PCell) but fails to receive the downlinkdata on component carrier 2 (SCell) (i.e., when the result of errordetection on component carrier 1 (PCell) is an ACK and the result oferror detection on component carrier 2 (SCell) is a NACK), the responsesignals are mapped to a PUCCH resource in PUCCH region 1 to beimplicitly signaled, while a first phase point (e.g., phase point (1, 0)and/or the like) is used as the phase point of the response signals. Inaddition, when terminal 1 succeeds in receiving the downlink data oncomponent carrier 1 (PCell) and also succeeds in receiving the downlinkdata on component carrier 2 (SCell), the response signals are mapped toa PUCCH resource in PUCCH region 2 while the first phase point is used.More specifically, when the number of downlink component carriers is twowhile there is a single codeword (CW) per downlink component carrier,the results of error detection are represented in four patterns (i.e.,ACK/ACK, ACK/NACK, NACK/ACK and NACK/NACK). The four patterns can berepresented by combinations of two PUCCH resources and two kinds ofphase points (e.g., binary phase shift keying (BPSK) mapping).

In addition, when terminal 1 fails to receive DCI on component carrier 1(PCell) but succeeds in receiving downlink data on component carrier 2(SCell) (i.e., the result of error detection on component carrier 1(PCell) is a DTX and the result of error detection on component carrier2 (SCell) is an ACK), the CCEs occupied by the PDCCH intended forterminal 1 cannot be identified. Thus, the PUCCH resource included inPUCCH region 1 and associated in a one-to-one correspondence with thetop CCE index of the CCEs cannot be identified either. Accordingly, inthis case, in order to report an ACK, which is the result of errordetection on component carrier 2, the response signals need to be mappedto an explicitly signaled PUCCH resource included in PUCCH region 2 (maybe referred to as “to support implicit signaling,” hereinafter).

To be more specific, FIG. 5 illustrates examples of mapping of patternsfor the results of error detection in the following cases: when thereare two downlink component carriers (one PCell and one SCell), and

(a) Single CW per downlink component carrier;

(b) Single CW for one of the downlink component carriers, and two CWsfor the other; and

(c) Two CWs per downlink component carrier. The number of patterns forresults of error detection for (a) is four (i.e., 22=4). The number ofpatterns for (b) is eight (i.e., 23=8). The number of patterns for (c)is 16 (i.e., 24=16). The number of PUCCH resources required for mappingall the patterns is at least one for (a), at least two for (b) and atleast four for (c) when the phase difference between phase points is aminimum of 90 degrees (i.e., when a maximum of four patterns per PUCCHresource is mapped).

In FIG. 5A, one PUCCH resource is sufficient when mapping is performedusing QPSK because there are only four patterns for results of errordetection. However, in order to improve the degree of freedom in mappingand the error rate in reporting response signals to the base station,BPSK mapping may be carried out using two PUCCH resources as illustratedin FIG. 5A. In the mapping illustrated in FIG. 5A, the base station candetermine the result of error detection on component carrier 2 (SCell)only by determining in which one of the PUCCH resources the responsesignals are reported.

Meanwhile, the base station cannot determine the result of errordetection on component carrier 1 (PCell) only by determining in whichone of the PUCCH resources the response signals are reported. The basestation can determine whether the result of error detection is an ACK orNACK further by determining to which pattern on BPSK the responsesignals are mapped.

As described, the method used by the base station to determine responsesignals varies depending on the mapping method. As a result, the errorrate characteristics vary for each set of response signals. To put itdifferently, determining the ACK or NACK by only determining in whichone of the PUCCH resources the response signals are reported(hereinafter, may be referred to as “determination method 1”) has fewererrors than determining the ACK or NACK by determining in which one ofthe PUCCH resources the response signals are reported and furtherdetermining the phase point of the PUCCH resource (hereinafter, may bereferred to as “determination method 2”).

Likewise, in FIG. 5B, the error rate characteristics of the set ofresponse signals for CW0 of component carrier 1 (PCell) indicate fewererrors than the error rate characteristics of the other two sets ofresponse signals. In FIG. 5C, the error rate characteristics of theresponse signals for two CWs (CW0, CW1) of component carrier 1 (PCell)indicate fewer errors than the error rate characteristics of theresponse signals for two CWs (CW0, CW1) of component carrier 2 (SCell).

Meanwhile, there is a period in which the understanding about the numberof CCs configured for a terminal is different between a base station andthe terminal (i.e., uncertainty period or misalignment period). The basestation notifies the terminal of a message indicating reconfiguration tochange the number of CCs, and upon reception of the message, theterminal understands that the number of CCs has been changed andnotifies the base station of a completion message for thereconfiguration of the number of CCs. The period in which theunderstanding about the number of CCs configured for a terminal isdifferent between a base station and the terminal stems from the factthat the base station understands, upon reception of the message, forthe first time, that the number of CCs configured for the terminal hasbeen changed.

For example, when the terminal understands that the number of CCsconfigured for the terminal is one while the base station understandsthat the number of CCs configured for the terminal is two, the terminaltransmits response signals for the data that has been received by theterminal, using the mapping pattern for the result of error detectioncorresponding to one CC. Meanwhile, the base station determines theresponse signals from the terminal for the data that has beentransmitted to the terminal, using the mapping pattern for the resultsof error detection corresponding to two CCs.

When the number of CCs is one, the mapping pattern for a result of errordetection for one CC that is used in the LTE system is used (may bereferred to as “LTE fallback,” hereinafter) in order to ensure backwardcompatibility with the LTE system. More specifically, when one CCperforms single-CW processing, an ACK is mapped to the phase point (−1,0) and a NACK is mapped to the phase point (1, 0) using BPSK mapping(may be referred to as “fallback to Format 1a,” hereinafter) asillustrated in FIG. 6A. As illustrated in 6B, when one CC performstwo-CW processing, ACK/ACK, ACK/NACK, NACK/ACK and NACK/NACK are mappedto the phase points (−1, 0), (0, 1), (0, −1), and (1, 0), respectively,using QPSK mapping (may be referred to as “fallback to Format 1b,”hereinafter).

To be more specific, a description will be provided using an example ofa case where the base station transmits one piece of single-CW data onPCell and one piece of single-CW data on SCell using the two CCs whenthe terminal understands that the number of CCs configured for theterminal is one while the base station understands that the number ofCCs configured for the terminal is two. Since the terminal understandsthat the number of CCs configured for the terminal is one, the terminalreceives only PCell. When succeeding in receiving the downlink data inPCell, the terminal maps the response signals using the mappingillustrated in FIG. 6A to the PUCCH resource in the uplink componentcarrier (PUCCH resource 1) associated in a one-to-one correspondencewith the top CCE index of the CCEs occupied by the PDCCH indicating thePDSCH in PCell (i.e., implicitly signaled). In short, the terminal usesthe phase point (−1, 0). Meanwhile, the base station determines theresponse signals using the mapping illustrated in FIG. 5A since the basestation understands that the number of CCs configured for the terminalis two. In other words, the base station can determine that single CW ofPCell is an ACK and single CW of SCell is a NACK or DTX because of thephase point (−1, 0) of PUCCH resource 1. Likewise, when failing toreceive the downlink data in PCell, the terminal needs to map theresponse signals to the phase point (1, 0).

The same applies to the case where the way the understanding about thenumber of CCs is different between the base station and the terminal isopposite to the case described above. To put it more specifically, thiscase is where the base station transmits one piece of single-CW data onPCell to the terminal using the one CC when the terminal understandsthat the number of CCs configured for the terminal is two while the basestation understands that the number of CCs configured for the terminalis one. Since the terminal understands that the number of CCs configuredfor the terminal is two, the terminal receives PCell and SCell. When theterminal succeeds in receiving the downlink data in PCell, the basestation expects to receive, using the mapping illustrated in FIG. 6A,the response signals mapped to the phase point (−1, 0) of the PUCCHresource in the uplink component carrier (PUCCH resource 1) associatedin a one-to-one correspondence with the top CCE index of the CCEsoccupied by the PDCCH indicating the PDSCH in PCell (implicitlysignaled). Accordingly, although the terminal understands that thenumber of CCs is two, the terminal needs to map the response signals tothe phase point (−1, 0) of PUCCH resource 1 as illustrated in FIG. 5Awhen single CW of PCell is an ACK and SCell is a DTX. Likewise, whenfailing to receive the downlink data in PCell, the terminal needs to mapthe response signals to the phase point (1, 0).

As described above, even when the understanding about the number of CCsconfigured for a terminal is different between a base station and theterminal, the response signals on PCell and SCell need to be correctlydetermined (may be referred to as “to support LTE fallback,”hereinafter).

FIG. 5A supports LTE fallback. More specifically, FIG. 5A supports LTEfallback to PUCCH format 1a. FIG. 5B does not support LTE fallbackbecause A/A/D is not mapped to the phase point (−1, 0) of PUCCH resource1 when PCell performs two-CW processing and SCell performs single-CWprocessing. More specifically, FIG. 5B does not support LTE fallback toPUCCH format 1a. In addition, FIG. 5B does not support LTE fallbackbecause A/D/D is not mapped to the phase point (−1, 0) of PUCCH resource1, A/N/D is not mapped to the phase point (0, 1) of PUCCH resource 1,and N/A/D is not mapped to the phase point (0, −1) either when PCellperforms single-CW processing and SCell performs two-CW processing. Morespecifically, FIG. 5B does not support LTE fallback to PUCCH format 1b.FIG. 5C does not support LTE fallback because A/A/D/D is not mapped tothe phase point (−1, 0) of PUCCH resource 1, A/N/D/D is not mapped tothe phase point (0, 1) of PUCCH resource 1, and N/A/D/D is not mapped tothe phase point (0, −1) of PUCCH resource 1 either. More specifically,FIG. 5C does not support LTE fallback to PUCCH format 1b.

In the mapping method disclosed in Non-Patent Literature (hereinafter,abbreviated as NPL) 8 (may be referred to as “transmission rule table”or “mapping table”) (FIGS. 7 and 8), two ACK/NACK bits (may be referredto as “HARQ-ACK” bit) (correspond to b0 and b1 in NPL 9) in case of“four ACK/NACK Bits” in FIG. 8, for example, can be always determined bydetermination method 1. However, the remaining two ACK/NACK bits(corresponding to b2 and b3 in NPL 9) in the “four ACK/NACK Bits” inFIG. 8 are always determined by determination method 2. An evaluationresult using the abovementioned mapping is disclosed in NPL 9, and itcan be seen that NACK-to-ACK characteristics of b2 and b3 are poor ascompared with b0 and b1.

In the mapping method disclosed in NPL 10 (FIG. 9), the number of PUCCHresources that can be determined by determination method 1 is smoothedout among the bits. More specifically, it is possible to determine b3 inPUCCH 1, b0 and b1 in PUCCH 2, b1 and b2 in PUCCH 3, and b3 in PUCCH 4by determination method 1. In FIG. 9, the number of PUCCH resources thatcan be determined by determination method 1 for each bit is one with b0,two with b1, one with b2 and two with b3. Furthermore, NPL 10 disclosesnothing about associations between PUCCH 1 and b0, PUCCH 2 and b1, PUCCH3 and b2, and PUCCH 4 with b3, but if they are associated with eachother, implicit signaling for an optional ACK/NACK bit is supported inNPL 10. However, this mapping cannot support LTE fallback in two CCs.

CITATION LIST Non-Patent Literatures

NPL 1 3GPP TS 36.211 V9.1.0, “Physical Channels and Modulation (Release9),” March 2010 NPL 2 3GPP TS 36.212 V9.2.0, “Multiplexing and channelcoding (Release 9),” June 2010 NPL 3 3GPP TS 36.213 V9.2.0, “Physicallayer procedures (Release 9),” June 2010 NPL 4 Seigo Nakao, TomofumiTakata, Daichi Imamura, and Katsuhiko Hiramatsu, “Performanceenhancement of E-UTRA uplink control channel in fast fadingenvironments,” Proceeding of IEEE VTC 2009 spring, April. 2009 NPL 5Ericsson and ST-Ericsson, “A/N transmission in the uplink for carrieraggregation,” R1-100909, 3GPP TSG-RAN WG1 #60, February 2010 NPL 6 ZTE,3GPP RAN1 meeting #57, R1-091702, “Uplink Control Channel Design forLTE-Advanced,” May 2009 NPL 7 Panasonic, 3GPP RAN1 meeting #57,R1-091744, “UL ACK/NACK transmission on PUCCH for Carrier aggregation,”May 2009 NPL 8 CATT, LG Electronics, Qualcomm Incorporated, ZTE, 3GPPRAN1 meeting, R1-104140, “ACK/NACK Multiplexing Simulation Assumptionsin Rel-10,” June 2010 NPL 9 CATT, 3GPP RAN1 meeting, R1-104314,“Equalization of ACK/NACK bit performance in LTE-A,” August 2010 NPL 10Panasonic, 3GPP RAN1 meeting #61, R1-102856, “Support of UL ACK/NACKchannel selection for carrier aggregation,” May 2010

BRIEF SUMMARY Technical Problem

In the channel selection described above, the method used by the basestation to determine response signals varies depending on the mappingmethod. As a result, the error rate characteristics vary for each set ofresponse signals.

In the case where the error rate characteristics vary for each set ofresponse signals, larger transmission power is required even for aterminal having strict restrictions on its transmission power when theterminal transmits response signals having poor error ratecharacteristics to the base station. In addition, the increase intransmission power in this case causes an increase in interference toother terminals.

In addition, as described above, the PUCCH resource in the uplinkcomponent carrier (e.g., PUCCH resource in PUCCH region 1 in FIG. 4)needs to be associated in a one-to-one correspondence with the top CCEindex of the CCEs occupied by the PDCCH indicating the PDSCH in PCC(PCell) (implicit signaling) in channel selection. When a terminal failsto receive the PDCCH indicating the PDSCH intended for the terminal inPCell, the terminal cannot identify the PUCCH resource in the uplinkcomponent carrier associated in a one-to-one correspondence with the topCCE index of the CCEs occupied by the PDCCH resulting in receptionfailure. For this reason, when the result of error detection on thePDSCH in PCell is a DTX, the mapping needs to be one that does not usethis PUCCH resource (i.e., supporting implicit signaling).

Moreover, considering the period in which the understanding about thenumber of CCs configured for a terminal is different between a basestation and the terminal (i.e., uncertainty period or misalignmentperiod), the mapping has to be one that supports LTE fallback. Inparticular, considering that a maximum of two CCs is mostly used in theintroductory phase of the LTE-A system, the mapping has to be one thatsupports LTE fallback when the number of CCs is two.

It is an object of the claimed invention to provide a terminal apparatusand a retransmission control method that make it possible to support LTEfallback from two CCs while improving the characteristics of responsesignals having poor transmission characteristics by smoothing out, amongthe bits, the number of PUCCH resources each allowing an ACK/NACK to bedetermined only by determining the PUCCH resources in which the responsesignals are reported in a case where ARQ is applied to communicationsusing an uplink component carrier and a plurality of downlink componentcarriers associated with the uplink component carrier while CCEs in aPDCCH region in PCell are associated in a one-to-one correspondence withPUCCH resources in the uplink component carrier.

Solution to Problem

A terminal apparatus according to an aspect of the claimed inventionincludes: a downlink data receiving section that receives downlink datatransmitted on at least one downlink data channel of a plurality ofdownlink component carriers; an error detecting section that detects thepresence or absence of a reception error in the received downlink data;a transmission section that transmits response signals using an uplinkcontrol channel of an uplink component carrier on the basis of a resultof error detection obtained by the error detecting section, in which aplurality of uplink control channel regions associated with theplurality of downlink component carriers are each defined by a resourcegroup defined by a plurality of sequences in the same time frequencyresource block, and the transmission section transmits the responsesignals using the uplink control channel allocated in any of theplurality of uplink control channel regions.

A retransmission control method according to an aspect of the claimedinvention comprising: receiving downlink data transmitted on at leastone downlink data channel of a plurality of downlink component carriers;detecting the presence or absence of a reception error in the receiveddownlink data; and transmitting response signals using an uplink controlchannel of an uplink component carrier on the basis of a result of theerror detection, in which a plurality of uplink control channel regionsrespectively associated with the plurality of downlink componentcarriers are each defined by a resource group defined by a plurality ofsequences in the same time frequency resource block, and the responsesignals are transmitted using the uplink control channel allocated inany of the plurality of uplink control channel regions.

Advantageous Effects of Invention

According to the claimed invention, it is possible to support LTEfallback from two CCs while improving the characteristics of responsesignals having poor transmission characteristics by smoothing out, amongthe bits, the number of PUCCH resources each allowing an ACK/NACK to bedetermined only by determining the PUCCH resource in which the responsesignals are reported in a case where ARQ is applied to communicationsusing an uplink component carrier and a plurality of downlink componentcarriers associated with the uplink component carrier while CCEs in aPDCCH region in PCell are associated in a one-to-one correspondence withPUCCH resources in the uplink component carrier.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram illustrating a method of spreading response signalsand reference signals;

FIG. 2 is a diagram illustrating an operation related to a case whereTDM is applied to response signals and uplink data on PUSCH resources;

FIGS. 3A and 3B are diagrams provided for describing asymmetric carrieraggregation and a control sequence applied to individual terminals;

FIG. 4 is a diagram provided for describing asymmetric carrieraggregation and a control sequence applied to individual terminals;

FIGS. 5A-5C represent diagram 1 provided for describing examples ofACK/NACK mapping;

FIGS. 6A and 6B represent diagram 2 provided for describing examples ofACK/NACK mapping;

FIG. 7 illustrates ACK/NACK mapping 1 disclosed in NPL 8;

FIG. 8 illustrates ACK/NACK mapping 2 disclosed in NPL 8;

FIG. 9 illustrates ACK/NACK mapping disclosed in NPL 10;

FIG. 10 is a block diagram illustrating a configuration of a basestation according to Embodiment 1 of the claimed invention;

FIG. 11 is a block diagram illustrating a configuration of a terminalaccording to Embodiment 1 of the claimed invention;

FIG. 12 illustrates control example 1 for PUCCH resources according toEmbodiment 1 of the claimed invention;

FIG. 13 illustrates control example 2 for PUCCH resources according toEmbodiment 1 of the claimed invention;

FIGS. 14A and 14B illustrate control example 1 for ACK/NACK mappingaccording to Embodiment 1 of the claimed invention;

FIG. 15 illustrates example 1 of an ACK/NACK mapping table according toEmbodiment 1 of the claimed invention;

FIG. 16 illustrates control example 3 for PUCCH resources according toEmbodiment 1 of the claimed invention;

FIGS. 17A and 17B illustrate control example 2 for ACK/NACK mappingaccording to Embodiment 1 of the claimed invention;

FIG. 18 illustrates example 2 of the ACK/NACK mapping table according toEmbodiment 1 of the claimed invention;

FIG. 19 illustrates control example 4 for PUCCH resources according toEmbodiment 1 of the claimed invention;

FIGS. 20A and 20B illustrate control example 3 for ACK/NACK mappingaccording to Embodiment 1 of the claimed invention;

FIG. 21 illustrates example 3 of the ACK/NACK mapping table according toEmbodiment 1 of the claimed invention;

FIGS. 22A and 22B illustrate control example 4 for ACK/NACK mappingaccording to Embodiment 1 of the claimed invention;

FIG. 23 illustrates example 4 of the ACK/NACK mapping table according toEmbodiment 1 of the claimed invention;

FIG. 24 illustrates example 5 of the ACK/NACK mapping table according toEmbodiment 1 of the claimed invention;

FIG. 25 illustrates example 6 of the ACK/NACK mapping table according toEmbodiment 1 of the claimed invention;

FIG. 26 illustrates example 7 of the ACK/NACK mapping table according toEmbodiment 1 of the claimed invention;

FIGS. 27A-27C illustrate a control example for ACK/NACK mappingaccording to Embodiment 2 of the claimed invention;

FIGS. 28A-28C illustrate an example of an ACK/NACK mapping tableaccording to Embodiment 2 of the claimed invention;

FIG. 29 is a diagram representing the number of CWs on PCell and thenumber of CWs on SCell and the number of ACK/NACK bits with each numberof downlink component carriers in Embodiment 2 of the claimed invention;

FIG. 30 is a diagram provided for describing reasons why implicitsignaling according to Embodiment 2 of the claimed invention cannot beused;

FIG. 31 illustrates a control example for PUCCH resources according toEmbodiment 2 of the claimed invention (case 6);

FIGS. 32A-32C illustrate an example of the ACK/NACK mapping tableaccording to Embodiment 2 of the claimed invention (case 6);

FIG. 33 illustrates a control example for PUCCH resources according toEmbodiment 2 of the claimed invention (case 7);

FIGS. 34A-34C illustrate an example of the ACK/NACK mapping tableaccording to Embodiment 2 of the claimed invention (case 7);

FIG. 35 illustrates a control example for PUCCH resources according toEmbodiment 2 of the claimed invention (case 8); and

FIGS. 36A and 36B illustrate an example of the ACK/NACK mapping tableaccording to Embodiment 2 of the claimed invention (case 8).

DETAILED DESCRIPTION Description of Embodiments

Hereinafter, embodiments of the claimed invention will be described indetail with reference to the accompanying drawings. Throughout theembodiments, the same elements are assigned the same reference numeralsand any duplicate description of the elements is omitted.

Embodiment 1

(Configuration of Base Station)

FIG. 10 is a configuration diagram of base station 100 according toEmbodiment 1 of the claimed invention.

In FIG. 10, base station 100 includes control section 101, controlinformation generating section 102, coding section 103, modulationsection 104, coding section 105, data transmission controlling section106, modulation section 107, mapping section 108, inverse fast Fouriertransform (IFFT) section 109, CP adding section 110, radio transmittingsection 111, radio receiving section 112, CP removing section 113, PUCCHextracting section 114, despreading section 115, sequence controllingsection 116, correlation processing section 117, A/N determining section118, bundled A/N despreading section 119, inverse discrete Fouriertransform (IDFT) section 120, bundled A/N determining section 121 andretransmission control signal generating section 122.

Control section 101 assigns a downlink resource for transmitting controlinformation (i.e., downlink control information assignment resource) anda downlink resource for transmitting downlink data (i.e., downlink dataassignment resource) for a resource assignment target terminal(hereinafter, referred to as “destination terminal” or simply“terminal”) 200. This resource assignment is performed in a downlinkcomponent carrier included in a component carrier group configured forresource assignment target terminal 200. In addition, the downlinkcontrol information assignment resource is selected from among theresources corresponding to downlink control channel (i.e., PDCCH) ineach downlink component carrier. Moreover, the downlink data assignmentresource is selected from among the resources corresponding to downlinkdata channel (i.e., PDSCH) in each downlink component carrier. Inaddition, when there are a plurality of resource assignment targetterminals 200, control section 101 assigns different resources toresource assignment target terminals 200, respectively.

The downlink control information assignment resources are equivalent toL1/L2 CCH described above. To put it more specifically, the downlinkcontrol information assignment resources are each formed of one or aplurality of CCEs (or R-CCEs, and may be referred to as “CCE” simply,without any distinction between CCE and R-CCE).

Control section 101 determines the coding rate used for transmittingcontrol information to resource assignment target terminal 200. The datasize of the control information varies depending on the coding rate.Thus, control section 101 assigns a downlink control informationassignment resource having the number of CCEs that allows the controlinformation having this data size to be mapped to the resource.

Control section 101 outputs information on the downlink data assignmentresource to control information generating section 102. Moreover,control section 101 outputs information on the coding rate to codingsection 103. In addition, control section 101 determines and outputs thecoding rate of transmission data (i.e., downlink data) to coding section105. Moreover, control section 101 outputs information on the downlinkdata assignment resource and downlink control information assignmentresource to mapping section 108. However, control section 101 controlsthe assignment in such a way that the downlink data and downlink controlinformation for the downlink data are mapped to the same downlinkcomponent carrier.

Control information generating section 102 generates and outputs controlinformation including the information on the downlink data assignmentresource to coding section 103. This control information is generatedfor each downlink component carrier. In addition, when there are aplurality of resource assignment target terminals 200, the controlinformation includes the terminal ID of each destination terminal 200 inorder to distinguish resource assignment target terminals 200 from oneanother. For example, the control information includes CRC bits maskedby the terminal ID of destination terminal 200. This control informationmay be referred to as “control information carrying downlink assignment”or “downlink control information (DCI).”

Coding section 103 encodes the control information using the coding ratereceived from control section 101 and outputs the coded controlinformation to modulation section 104.

Modulation section 104 modulates the coded control information andoutputs the resultant modulation signals to mapping section 108.

Coding section 105 uses the transmission data (i.e., downlink data) foreach destination terminal 200 and the coding rate information fromcontrol section 101 as input and encodes and outputs the transmissiondata to data transmission controlling section 106. However, when aplurality of downlink component carriers are assigned to destinationterminal 200, coding section 105 encodes each piece of transmission datato be transmitted on a corresponding one of the downlink componentcarriers and transmits the coded pieces of transmission data to datatransmission controlling section 106.

Data transmission controlling section 106 outputs the coded transmissiondata to modulation section 107 and also keeps the coded transmissiondata at the initial transmission. Data transmission controlling section106 keeps the coded transmission data for each destination terminal 200.In addition, data transmission controlling section 106 keeps thetransmission data for one destination terminal 200 for each downlinkcomponent carrier on which the transmission data is transmitted. Thus,it is possible to perform not only retransmission control for overalldata transmitted to destination terminal 200, but also retransmissioncontrol for data on each downlink component carrier.

Furthermore, upon reception of a NACK or DTX for downlink datatransmitted on a certain downlink component carrier from retransmissioncontrol signal generating section 122, data transmission controllingsection 106 outputs the data kept in the manner described above andcorresponding to this downlink component carrier to modulation section107. Upon reception of an ACK for the downlink data transmitted on acertain downlink component carrier from retransmission control signalgenerating section 122, data transmission controlling section 106deletes the data kept in the manner described above and corresponding tothis downlink component carrier.

Modulation section 107 modulates the coded transmission data receivedfrom data transmission controlling section 106 and outputs the resultantmodulation signals to mapping section 108.

Mapping section 108 maps the modulation signals of the controlinformation received from modulation section 104 to the resourceindicated by the downlink control information assignment resourcereceived from control section 101 and outputs the resultant modulationsignals to IFFT section 109.

Mapping section 108 maps the modulation signals of the transmission datareceived from modulation section 107 to the resource (i.e., PDSCH (i.e.,downlink data channel)) indicated by the downlink data assignmentresource received from control section 101 (i.e., information includedin the control information) and outputs the resultant modulation signalsto IFFT section 109.

The control information and transmission data mapped to a plurality ofsubcarriers in a plurality of downlink component carriers in mappingsection 108 is transformed into time-domain signals fromfrequency-domain signals in IFFT section 109, and CP adding section 110adds a CP to the time-domain signals to form OFDM signals. The OFDMsignals undergo transmission processing such as digital to analog (D/A)conversion, amplification and up-conversion and/or the like in radiotransmitting section 111 and are transmitted to terminal 200 via anantenna.

Radio receiving section 112 receives, via an antenna, the uplinkresponse signals or reference signals transmitted from terminal 200, andperforms reception processing such as down-conversion, A/D conversionand/or the like on the uplink response signals or reference signals.

CP removing section 113 removes the CP added to the uplink responsesignals or reference signals from the uplink response signals orreference signals that have undergone the reception processing.

PUCCH extracting section 114 extracts, from the PUCCH signals includedin the received signals, the signals in the PUCCH region correspondingto the bundled ACK/NACK resource previously reported to terminal 200.The bundled ACK/NACK resource herein refers to a resource used fortransmission of the bundled ACK/NACK signals and adopting the DFT-S-OFDMformat structure. To put it more specifically, PUCCH extracting section114 extracts the data part of the PUCCH region corresponding to thebundled ACK/NACK resource (i.e., SC-FDMA symbols on which the bundledACK/NACK resource is assigned) and the reference signal part of thePUCCH region (i.e., SC-FDMA symbols on which the reference signals fordemodulating the bundled ACK/NACK signals are assigned). PUCCHextracting section 114 outputs the extracted data part to bundled A/Ndespreading section 119 and outputs the reference signal part todespreading section 115-1.

In addition, PUCCH extracting section 114 extracts, from the PUCCHsignals included in the received signals, a plurality of PUCCH regionscorresponding to an A/N resource associated with a CCE that has beenoccupied by the PDCCH used for transmission of the downlink assignmentcontrol information (DCI), and corresponding to a plurality of A/Nresources previously reported to terminal 200. The A/N resource hereinrefers to the resource to be used for transmission of an A/N. To put itmore specifically, PUCCH extracting section 114 extracts the data partof the PUCCH region corresponding to the A/N resource (i.e., SC-FDMAsymbols on which the uplink control signals are assigned) and thereference signal part of the PUCCH region (i.e., SC-FDMA symbols onwhich the reference signals for demodulating the uplink control signalsare assigned). PUCCH extracting section 114 outputs both of theextracted data part and reference signal part to despreading section115-2. In this manner, the response signals are received on the resourceselected from the PUCCH resource associated with the CCE and thespecific PUCCH resource previously reported to terminal 200.

Sequence controlling section 116 generates a base sequence that may beused for spreading each of the A/N reported from terminal 200, thereference signals for the A/N, and the reference signals for the bundledACK/NACK signals (i.e., length-12 ZAC sequence). In addition, sequencecontrolling section 116 identifies a correlation window corresponding toa resource on which the reference signals may be assigned (hereinafter,referred to as “reference signal resource”) in PUCCH resources that maybe used by terminal 200. Sequence control section 116 outputs theinformation indicating the correlation window corresponding to thereference signal resource on which the reference signals may be assignedin bundled ACK/NACK resources and the base sequence to correlationprocessing section 117-1. Sequence controlling section 116 outputs theinformation indicating the correlation window corresponding to thereference signal resource and the base sequence to correlationprocessing section 117-1. In addition, sequence controlling section 116outputs the information indicating the correlation window correspondingto the A/N resources on which an A/N and the reference signals for theA/N are assigned and the base sequence to correlation processing section117-2.

Despreading section 115-1 and correlation processing section 117-1perform processing on the reference signals extracted from the PUCCHregion corresponding to the bundled ACK/NACK resource.

To put it more specifically, despreading section 115-1 despreads thereference signal part using a Walsh sequence to be used insecondary-spreading for the reference signals of the bundled ACK/NACKresource by terminal 200 and outputs the despread signals to correlationprocessing section 117-1.

Correlation processing section 117-1 uses the information indicating thecorrelation window corresponding to the reference signal resource andthe base sequence and thereby finds a correlation value between thesignals received from despreading section 115-1 and the base sequencethat may be used in primary-spreading in terminal 200. Correlationprocessing section 117-1 outputs the correlation value to bundled A/Ndetermining section 121.

Despreading section 115-2 and correlation processing section 117-2perform processing on the reference signals and A/Ns extracted from theplurality of PUCCH regions corresponding to the plurality of A/Nresources.

To put it more specifically, despreading section 115-2 despreads thedata part and reference signal part using a Walsh sequence and a DFTsequence to be used in secondary-spreading for the data part andreference signal part of each of the A/N resources by terminal 200, andoutputs the despread signals to correlation processing section 117-2.

Correlation processing section 117-2 uses the information indicating thecorrelation window corresponding to each of the A/N resources and thebase sequence and thereby finds a correlation value between the signalsreceived from despreading section 115-2 and a base sequence that may beused in primary-spreading by terminal 200. Correlation processingsection 117-2 outputs each correlation value to A/N determining section118.

A/N determining section 118 determines, on the basis of the plurality ofcorrelation values received from correlation processing section 117-2,which of the A/N resources is used to transmit the signals from terminal200 or none of the A/N resources is used. When determining that thesignals are transmitted using one of the A/N resources from terminal200, A/N determining section 118 performs coherent detection using acomponent corresponding to the reference signals and a componentcorresponding to the A/N and outputs the result of coherent detection toretransmission control signal generating section 122. Meanwhile, whendetermining that terminal 200 uses none of the A/N resources, A/Ndetermining section 118 outputs the determination result indicating thatnone of the A/N resources is used to retransmission control signalgenerating section 122. The details of mapping of an A/N phase pointused in A/N determination will be described, hereinafter.

Bundled A/N despreading section 119 despreads, using a DFT sequence, thebundled ACK/NACK signals corresponding to the data part of the bundledACK/NACK resource received from PUCCH extracting section 114 and outputsthe despread signals to IDFT section 120.

IDFT section 120 transforms the bundled ACK/NACK signals in thefrequency-domain received from bundled A/N despreading section 119 intotime-domain signals by IDFT processing and outputs the bundled ACK/NACKsignals in the time-domain to bundled A/N determining section 121.

Bundled A/N determining section 121 demodulates the bundled ACK/NACKsignals corresponding to the data part of the bundled ACK/NACK resourcereceived from IDFT section 120, using the reference signal informationon the bundled ACK/NACK signals that is received from correlationprocessing section 117-1. In addition, bundled A/N determination section121 decodes the demodulated bundled ACK/NACK signals and outputs theresult of decoding to retransmission control signal generating section122 as the bundled A/N information. However, when the correlation valuereceived from correlation processing section 117-1 is smaller than athreshold, and bundled A/N determining section 121 thus determines thatterminal 200 does not use any bundled A/N resource to transmit thesignals, bundled A/N determining section 121 outputs the result ofdetermination to retransmission control signal generating section 122.

Retransmission control signal generating section 122 determines whetheror not to retransmit the data transmitted on the downlink componentcarrier (i.e., downlink data) on the basis of the information receivedfrom bundled A/N determining section 121 and the information receivedfrom A/N determining section 118 and generates retransmission controlsignals based on the result of determination. To put it morespecifically, when determining that downlink data transmitted on acertain downlink component carrier needs to be retransmitted,retransmission control signal generating section 122 generatesretransmission control signals indicating a retransmission command forthe downlink data and outputs the retransmission control signals to datatransmission controlling section 106. In addition, when determining thatthe downlink data transmitted on a certain downlink component carrierdoes not need to be retransmitted, retransmission control signalgenerating section 122 generates retransmission control signalsindicating not to retransmit the downlink data transmitted on thedownlink component carrier and outputs the retransmission controlsignals to data transmission controlling section 106.

(Configuration of Terminal)

FIG. 11 is a block diagram illustrating a configuration of terminal 200according to Embodiment 1. In FIG. 11, terminal 200 includes radioreceiving section 201, CP removing section 202, fast Fourier transform(FFT) section 203, extraction section 204, demodulation section 205,decoding section 206, determination section 207, control section 208,demodulation section 209, decoding section 210, CRC section 211,response signal generating section 212, coding and modulation section213, primary-spreading sections 214-1 and 214-2, secondary-spreadingsections 215-1 and 215-2, DFT section 216, spreading section 217, IFFTsections 218-1, 218-2 and 218-3, CP adding sections 219-1, 219-2 and219-3, time-multiplexing section 220, selection section 221 and radiotransmitting section 222.

Radio receiving section 201 receives, via an antenna, OFDM signalstransmitted from base station 100 and performs reception processing suchas down-conversion, A/D conversion and/or the like on the received OFDMsignals. It should be noted that, the received OFDM signals includePDSCH signals assigned to a resource in a PDSCH (i.e., downlink data),or PDCCH signals assigned to a resource in a PDCCH.

CP removing section 202 removes a CP that has been added to the OFDMsignals from the OFDM signals that have undergone the receptionprocessing.

FFT section 203 transforms the received OFDM signals intofrequency-domain signals by FFT processing and outputs the resultantreceived signals to extraction section 204.

Extraction section 204 extracts, from the received signals to bereceived from FFT section 203, downlink control channel signals (i.e.,PDCCH signals) in accordance with coding rate information to bereceived. To put it more specifically, the number of CCEs (or R-CCEs)forming a downlink control information assignment resource variesdepending on the coding rate. Thus, extraction section 204 uses thenumber of CCEs that corresponds to the coding rate as units ofextraction processing, and extracts downlink control channel signals. Inaddition, the downlink control channel signals are extracted for eachdownlink component carrier. The extracted downlink control channelsignals are outputted to demodulation section 205.

Extraction section 204 extracts downlink data (i.e., downlink datachannel signals (i.e., PDSCH signals)) from the received signals on thebasis of information on the downlink data assignment resource intendedfor terminal 200 to be received from determination section 207 to bedescribed, hereinafter, and outputs the downlink data to demodulationsection 209. As described above, extraction section 204 receives thedownlink assignment control information (i.e., DCI) mapped to the PDCCHand receives the downlink data on the PDSCH.

Demodulation section 205 demodulates the downlink control channelsignals received from extraction section 204 and outputs the obtainedresult of demodulation to decoding section 206.

Decoding section 206 decodes the result of demodulation received fromdemodulation section 205 in accordance with the received coding rateinformation and outputs the obtained result of decoding to determinationsection 207.

Determination section 207 performs blind-determination (i.e.,monitoring) to find out whether or not the control information includedin the result of decoding received from decoding section 206 is thecontrol information intended for terminal 200. This determination ismade in units of decoding results corresponding to the units ofextraction processing. For example, determination section 207 demasksthe CRC bits by the terminal ID of terminal 200 and determines that thecontrol information resulted in CRC=OK (no error) as the controlinformation intended for terminal 200. Determination section 207 outputsinformation on the downlink data assignment resource intended forterminal 200, which is included in the control information intended forterminal 200, to extraction section 204.

In addition, when detecting the control information (i.e., downlinkassignment control information) intended for terminal 200, determinationsection 207 informs control section 208 that ACK/NACK signals will begenerated (or are present). Moreover, when detecting the controlinformation intended for terminal 200 from PDCCH signals, determinationsection 207 outputs information on a CCE that has been occupied by thePDCCH to control section 208.

Control section 208 identifies the A/N resource associated with the CCEon the basis of the information on the CCE received from determinationsection 207. Control section 208 outputs, to primary-spreading section214-1, a base sequence and a cyclic shift value corresponding to the A/Nresource associated with the CCE or the A/N resource previously reportedby base station 100, and also outputs a Walsh sequence and a DFTsequence corresponding to the A/N resource to secondary-spreadingsection 215-1. In addition, control section 208 outputs the frequencyresource information on the A/N resource to IFFT section 218-1.

When determining to transmit bundled ACK/NACK signals using a bundledACK/NACK resource, control section 208 outputs the base sequence andcyclic shift value corresponding to the reference signal part (i.e.,reference signal resource) of the bundled ACK/NACK resource previouslyreported by base station 100 to primary-despreading section 214-2 andoutputs a Walsh sequence to secondary-despreading section 215-2. Inaddition, control section 208 outputs the frequency resource informationon the bundled ACK/NACK resource to IFFT section 218-2.

Control section 208 outputs a DFT sequence used for spreading the datapart of the bundled ACK/NACK resource to spreading section 217 andoutputs the frequency resource information on the bundled ACK/NACKresource to IFFT section 218-3.

Control section 208 selects the bundled ACK/NACK resource or the A/Nresource and instructs selection section 221 to output the selectedresource to radio transmitting section 222. Moreover, control section208 instructs response signal generating section 212 to generate thebundled ACK/NACK signals or the ACK/NACK signals in accordance with theselected resource. The method of determining the A/N resource (i.e.,PUCCH resource) in control section 208 will be described in detail,hereinafter.

Demodulation section 209 demodulates the downlink data received fromextraction section 204 and outputs the demodulated downlink data todecoding section 210.

Decoding section 210 decodes the downlink data received fromdemodulation section 209 and outputs the decoded downlink data to CRCsection 211.

CRC section 211 performs error detection on the decoded downlink datareceived from decoding section 210, for each downlink component carrierusing CRC and outputs an ACK when CRC=OK (no error) or outputs a NACKwhen CRC=Not OK (error) to response signal generating section 212.Moreover, CRC section 211 outputs the decoded downlink data as thereceived data when CRC=OK (no error).

Response signal generating section 212 generates response signals on thebasis of the reception condition of downlink data (i.e., result of errordetection on downlink data) on each downlink component carrier receivedfrom CRC section 211. To put it more specifically, when instructed togenerate the bundled ACK/NACK signals from control section 208, responsesignal generating section 212 generates the bundled ACK/NACK signalsincluding the results of error detection for the respective componentcarriers as individual pieces of data. Meanwhile, when instructed togenerate ACK/NACK signals from control section 208, response signalgenerating section 212 generates ACK/NACK signals of one symbol.Response signal generating section 212 outputs the generated responsesignals to coding and modulation section 213. The details of the methodof generating ACK/NACK signals in response signal generating section 212will be described, hereinafter.

Upon reception of the bundled ACK/NACK signals, coding and modulationsection 213 encodes and modulates the received bundled ACK/NACK signalsto generate the modulation signals of 12 symbols and outputs themodulation signals to DFT section 216. In addition, upon reception ofthe ACK/NACK signals of one symbol, coding and modulation section 213modulates the ACK/NACK signals and outputs the modulation signals toprimary-spreading section 214-1.

DFT section 216 performs DFT processing on 12 time-series sets ofreceived bundled ACK/NACK signals to obtain 12 signal components in thefrequency-domain. DFT section 216 outputs the 12 signal components tospreading section 217.

Spreading section 217 spreads the 12 signal components received from DFTsection 216 using a DFT sequence indicated by control section 208 andoutputs the spread signal components to IFFT section 218-3.

Primary-spreading sections 214-1 and 214-2 corresponding to the A/Nresource and the reference signal resource of bundled ACK/NACK resourcespread ACK/NACK signals or reference signals using a base sequencecorresponding to the resource in accordance with an instruction fromcontrol section 208 and outputs the spread signals tosecondary-spreading sections 215-1 and 215-2.

Secondary-spreading sections 215-1 and 215-2 spread the receivedprimary-spread signals using a Walsh sequence or a DFT sequence inaccordance with an instruction from control section 208 and outputs thespread signals to IFFT sections 218-1 and 218-2.

IFFT sections 218-1, 218-2 and 218-3 perform IFFT processing on thereceived signals in association with the frequency positions where thesignals are to be allocated, in accordance with an instruction fromcontrol section 208. Accordingly, the signals inputted to IFFT sections218-1, 218-2 and 218-3 (i.e., ACK/NACK signals, the reference signals ofA/N resource, the reference signals of bundled ACK/NACK resource andbundled ACK/NACK signals) are transformed into time-domain signals.

CP adding sections 219-1, 219-2 and 219-3 add the same signals as thelast part of the signals obtained by IFFT processing to the beginning ofthe signals as a CP.

Time-multiplexing section 220 time-multiplexes the bundled ACK/NACKsignals received from CP adding section 219-3 (i.e., signals transmittedusing the data part of the bundled ACK/NACK resource) and the referencesignals of the bundled ACK/NACK resource to be received from CP addingsection 219-2 on the bundled ACK/NACK resource and outputs themultiplexed signals to selection section 221.

Selection section 221 selects one of the bundled ACK/NACK resourcereceived from time-multiplexing section 220 and the A/N resourcereceived from CP adding section 219-1 and outputs the signals assignedto the selected resource to radio transmitting section 222.

Radio transmitting section 222 performs transmission processing such asD/A conversion, amplification and up-conversion and/or the like on thesignals received from selection section 221 and transmits the resultantsignals to base station 100 via an antenna.

(Operations of Base Station 100 and Terminal 200)

A description will be provided regarding operations of base station 100and terminal 200 each configured in the manner described above.

Hereinafter, a description will be provided regarding the method ofdetermining the A/N resource (i.e., PUCCH resource) used fortransmission of response signals and the method of generating ACK/NACKsignals (mapping method) in control examples 1 to 5.

Control Example 1: Two-CW Processing for PCell, Two-CW Processing forSCell, and Cross-Carrier Scheduling from PCell to SCell

In FIG. 12, the method of determining the A/N resource (i.e., PUCCHresource) when both of PCell and SCell perform two-CW processing andcross-carrier scheduling is applied when the number of CCs is two. FIG.12 illustrates an example of cross-carrier scheduling from PCell toSCell, however. More specifically, the PDCCH in PCell indicates thePDSCH in SCell.

In FIG. 12, PUCCH resource 1 in an uplink component carrier is assignedin association in a one-to-one correspondence with the top CCE index(n_CCE) of the CCEs occupied by the PDCCH indicating the PDSCH in PCell(implicit signaling). Moreover, in FIG. 12, PUCCH resource 2 in theuplink component carrier is assigned in association in a one-to-onecorrespondence with the index subsequent to the top CCE index (n_CCE+1)of the CCEs occupied by the PDCCH indicating the PDSCH in PCell(implicit signaling).

In FIG. 12, PUCCH resource 3 in the uplink component carrier is assignedin association in a one-to-one correspondence with the top CCE index(n_CCE′ (n_CCE′≠n_CCE)) of the CCEs occupied by the PDCCH in PCell thatindicates the PDSCH in SCell. PUCCH resource 3 is cross-carrierscheduled from PCell to SCell. In FIG. 12, PUCCH resource 4 in theuplink component carrier assigned in association in a one-to-onecorrespondence with the index subsequent to the top CCE index (n_CCE′+1)of the CCEs occupied by the PDCCH indicating the PDSCH in PCell(implicit signaling).

It should be noted that, when cross-carrier scheduling is configuredfrom first SCell to second SCell, PUCCH resources 3 and 4 describedabove may be previously reported by the base station (explicitsignaling). In addition, when no cross-carrier scheduling is configured,PUCCH resources 3 and 4 described above may be previously reported bythe base station, likewise (explicit signaling).

It should be noted that, the PUCCH resources except for PUCCH resource 1(i.e., PUCCH resources 2, 3 and 4) may be previously reported from thebase station (explicit signaling). PUCCH resource 1 herein is associatedin a one-to-one correspondence with the CCE index (n_CCE) of the CCEsoccupied by the PDCCH indicating the PDSCH in PCell.

FIGS. 14 and 15 illustrate the method of generating ACK/NACK signalswhen both of PCell and SCell perform two-CW processing when the numberof CCs is two. PUCCH resources 1, 2, 3 and 4 in FIGS. 14 and 15correspond to PUCCH resources 1, 2, 3 and 4 illustrated in FIG. 12,respectively. The bits forming a combination of a plurality of an ACK,NACK and/or DTX are termed as bits b0, b1, b2 and b3 in sequence. Inaddition, bits b0, b1, b2 and b3 are respectively associated with theACK/NACK signals of CW0 of the PDSCH in PCell, ACK/NACK signals of CW1of the PDSCH in PCell, ACK/NACK signals of CW0 of the PDSCH in SCell,and ACK/NACK signals of CW1 of the PDSCH in SCell. The associationsbetween the bits and ACK/NACK signals are by no means limited to theabovementioned example.

The response signals for all the PUCCH resources are mapped to fourphase points regardless of a pattern for results of error detectionindicating a DTX. In addition, the response signals are mapped to thephase point for each of the PUCCH resources in a way that makes theHamming distance between adjacent phase points smaller (i.e., in a waythat makes the mapping closer to the Gray mapping).

FIG. 14B illustrates concentration of ACK/NACKs for PUCCH resources 1,2, 3 and 4 for bits b0, b1, b2 and b3 in FIG. 14A. For example, bit b1includes one ACK and three NACKs mapped for PUCCH resource 3 withreference to FIG. 14A. These parts of FIG. 14A correspond to “1, 3” inFIG. 14B, where the row of “b1” and the column of “PUCCH resource 3”intersect. In addition, the column of “the number of combinations forA:N=1:0 or 0:1” indicates how many combinations of “four ACKs and zeroNACK” (A:N=1:0(=4:0)) or “zero ACK and four NACKs” (A:N=0:1(=0:4)) foreach of the PUCCH resources are present. Moreover, in FIG. 14B, thecolumn of “A/N concentration” indicates the sum of the absolute valuesof differences between the number of ACKs and the number of NACKs in therespective PUCCH resources for all the PUCCH resources.

As described above, there are the two methods of determining responsesignals for base stations depending on the mapping methods. Morespecifically, base station use the method of determining the PUCCHresource on which the response signals are reported (i.e., determinationmethod 1) and the method of determining the PUCCH resource on which theresponse signal are reported and further determining the phase point ofthe PUCCH resource (i.e., determination method 2).

FIG. 14 illustrate the mapping method that smooths out (i.e.,equalizes), among the bits, the number of PUCCH resources each allowingthe ACK/NACK to be determined using determination method 1 and thatsupports implicit signaling for an optional ACK/NACK bit and LTEfallback (i.e., fallback to Format 1b in FIG. 14). This mapping methodis disclosed in Embodiment 1. FIG. 15 illustrates an ACK/NACK mappingtable (i.e., transmission rule table) corresponding to FIG. 14.

The PUCCH resource allowing the ACK/NACK to be determined usingdetermination method 1 herein is the PUCCH resource corresponding to thecombination for A:N=1:0(=4:0) or A:N=0:1(=0:4) in FIG. 14B. In addition,the number of PUCCH resources each allowing the ACK/NACK to bedetermined using determination method 1 is “the number of combinationsfor A:N=1:0 or 0:1” in FIG. 14B. Moreover, the smoothing out means toperform mapping that makes the difference between the maximum andminimum values of “the number of combinations for A:N=1:0 or 0:1” notgreater than one. More specifically, in the mapping illustrated in FIG.14, “the number of combinations for A:N=1:0 or 0:1” is two for two bits(b0 and b2) and one for the remaining two bits (b1 and b3) in a casewhere PCell performs two-CW processing and SCell also performs two-CWprocessing when the number of CCs is two. Accordingly, the differencebetween the maximum and minimum values is one in this mapping.

In other words, supporting implicit signaling for an optional ACK/NACKbit means that bit b0 associated with ACK/NACK of CW0 of PCell takes noDTX for mapping in PUCCH resource 1 associated with the top CCE index(n_CCE) of the CCEs occupied by the PDCCH indicating the PDSCH in PCellin FIG. 14A. Likewise, supporting implicit signaling for an optionalACK/NACK bit means that bit b1 takes no DTX for mapping in PUCCHresource 2, while bit b2 takes no DTX for mapping in PUCCH resource 3,and bit b3 takes no DTX for mapping in PUCCH resource 4.

It should be noted that, FIG. 14 illustrate an example in which all thePUCCH resources are implicitly signaled, so that implicit signaling foran optional ACK/NACK bit is supported in this example, but the PUCCHresources other than PUCCH resource 1 may be explicitly signaled. Inthis case, implicit signaling for at least one ACK/NACK bit may besupported.

Supporting LTE fallback means that the following conditions described as(1) to (3) are satisfied simultaneously. In a certain PUCCH resource,certain two bits satisfy A:N=0:1 (=0:4) and the remaining two bitscorrespond to the mapping illustrated in FIG. 6B (1). The remaining twobits in (1) are associated with two CWs processed by PDSCH in PCell (2).The PUCCH resource in which the condition (1) is satisfied is a PUCCHresource assigned in association in a one-to-one correspondence with thetop CCE index (n_CCE) of the CCEs occupied by the PDCCH indicating thePDSCH in PCell (i.e., PUCCH resource 1 in the example illustrated inFIG. 14) (3).

It should be noted that, the mapping in FIG. 14A is an example, and themapping in which bit b0 and bit b1 are switched may be used, forexample, since the mapping only needs to satisfy the conditions (1) to(3) simultaneously. In addition, the mapping for the PUCCH resourcesother than PUCCH resource 1 supporting LTE fallback may be rotated by 90degrees, 180 degrees, and 270 degrees in the clockwise direction,respectively, for example. Moreover, bit switching control may beperformed according to the priorities of CWs. For example, a CW having ahigher priority is preferentially assigned to bit b0 over bit b1 andalso to bit b2 over bit b3. Thus, ACK/NACK signals can be reported to abase station while ACK/NACK signals for a CW having a higher priority isassigned to a bit having a lower error rate.

As described above, it is possible to support implicit signaling foroptional response signals and LTE fallback (fallback to Format 1b inFIG. 14, to be more specific) from two CCs while improving thecharacteristics of response signals having poor transmissioncharacteristics by smoothing out, among the bits, the number of PUCCHresources each allowing the ACK/NACK to be determined only bydetermining the PUCCH resource in which the response signals arereported.

Control Example 2: Two-CW Processing for PCell, Single-CW Processing forSCell, and Cross-Carrier Scheduling from PCell to SCell

FIG. 16 illustrates a method of determining the A/N resource (i.e.,PUCCH resource) when PCell performs two-CW processing and SCell performssingle-CW processing and cross-carrier scheduling is applied when thenumber of CCs is two. FIG. 16 illustrates an example of cross-carrierscheduling from PCell to SCell, however. More specifically, the PDCCH inPCell indicates the PDSCH in SCell.

In FIG. 16, PUCCH resource 1 is assigned in association in a one-to-onecorrespondence with the top CCE index (n_CCE) of the CCEs occupied bythe PDCCH indicating the PDSCH in PCell (implicit signaling). Inaddition, in FIG. 16, PUCCH resource 2 is assigned in association in aone-to-one correspondence with the CCE index subsequent to the top CCEindex (n_CCE+1) of the CCEs occupied by the PDCCH indicating the PDSCHin PCell (implicit signaling).

In FIG. 16, PUCCH resource 3 in an uplink component carrier is assignedin association in a one-to-one correspondence with the top CCE index(n_CCE′) of the CCEs occupied by the PDCCH in PCell that indicates thePDSCH in SCell (implicit signaling). PUCCH resource 3 is cross-carrierscheduled from PCell to SCell.

It should be noted that, when cross-carrier scheduling is configuredfrom first SCell to second SCell, PUCCH resource 3 described above maybe previously reported by the base station (explicit signaling). Inaddition, when no cross-carrier scheduling is configured, PUCCH resource3 may be previously reported by the base station, likewise (explicitsignaling).

It should be noted that the PUCCH resources except for PUCCH resource 1associated in a one-to-one correspondence with the CCE index (n_CCE) ofthe CCEs occupied by the PDCCH indicating the PDSCH in PCell (i.e.,PUCCH resources 2 and 3) may be previously reported from the basestation (explicit signaling).

FIGS. 17 and 18 illustrate the method of generating (mapping) ACK/NACKsignals when PCell performs two-CW processing and SCell performssingle-CW processing when the number of CCs is two. PUCCH resources 1, 2and 3 in FIGS. 17 and 18 correspond to PUCCH resources 1, 2 and 3illustrated in FIG. 16, respectively. The bits forming a combination ofa plurality of an ACK and/or NACK and/or DTX are termed as bits b0, b1and b2 in sequence. In addition, bits b0, b1 and b2 are respectivelyassociated with ACK/NACK signals of CW0 of the PDSCH in PCell, ACK/NACKsignals of CW1 of the PDSCH in PCell and ACK/NACK signals of CW0 of thePDSCH in SCell. In other words, bits b0 and b1 are associated with theCell that performs two-CW processing and b2 is associated with the Cellthat performs single-CW processing. The associations between the bitsand ACK/NACK signals are by no means limited to the abovementionedexample.

In PUCCH resource 1 illustrated in FIG. 17A, the response signals aremapped to three phase points excluding the pattern of results of errordetection indicating a DTX. In PUCCH resource 2 illustrated in FIG. 17A,the response signals are mapped to three phase points regardless of anypattern for results of error detection indicating a DTX. In PUCCHresource 3 illustrated in FIG. 17A, the response signals are mapped totwo phase points. In addition, the response signals are mapped to thephase point for each of the PUCCH resources in a way that makes theHamming distance between adjacent phase points smaller (i.e., in a waythat makes the mapping closer to the Gray mapping).

FIG. 17B illustrates concentration of ACK/NACKs for PUCCH resources 1, 2and 3 for bits b0, b1 and b2 in FIG. 17A.

As described above, base stations use the two methods of determiningresponse signals depending on the mapping methods. More specifically,base station uses the method of determining the PUCCH resource in whichthe response signals are reported (determination method 1) and themethod of determining the PUCCH resource in which the response signalsare reported and further determining the phase point of the PUCCHresource (determination method 2).

FIG. 17 illustrate the mapping method that smooths out, among the bits,the number of PUCCH resources each allowing the ACK/NACK to bedetermined with determination method 1 and that supports implicitsignaling for an optional ACK/NACK bit and LTE fallback (i.e., fallbackto Format 1b in FIG. 17). This mapping method is disclosed inEmbodiment 1. FIG. 18 illustrates an ACK/NACK mapping table(transmission rule table) corresponding to FIG. 17.

The PUCCH resource allowing the ACK/NACK to be determined usingdetermination method 1 herein is the PUCCH resource corresponding to thecombination for A:N=1:0(=3:0) or A:N=0:1(=0:3=0:2) in FIG. 17B. Inaddition, the number of PUCCH resources each allowing the ACK/NACK to bedetermined using determination method 1 is “the number of combinationsfor A:N=1:0 or 0:1” in FIG. 17B. Moreover, the smoothing out means toperform mapping that makes the difference between the maximum andminimum values of “the number of combinations for A:N=1:0 or 0:1” notgreater than one. More specifically, in the mapping illustrated in FIG.17, “the number of combinations for A:N=1:0 or 0:1” is two for one bit(b2) and one for the remaining two bits (b0 and b1) in a case wherePCell performs two-CW processing and SCell also performs single-CWprocessing when the number of CCs is two. Accordingly, the differencebetween the maximum and minimum values is one in this mapping.

In other words, supporting implicit signaling for an optional ACK/NACKbit means that bit b0 associated with ACK/NACK of CW0 of PCell takes noDTX for mapping in PUCCH resource 1 associated with the top CCE index(n_CCE) of the CCEs occupied by the PDCCH indicating the PDSCH in PCellin FIG. 17A. Likewise, supporting implicit signaling for an optionalACK/NACK bit means that the bit b1 takes no DTX for mapping in PUCCHresource 2, and the bit b2 takes no DTX for mapping in PUCCH resource 3.

It should be noted that, FIG. 17 illustrate an example in which all thePUCCH resources are implicitly signaled, so that implicit signaling foran optional ACK/NACK bit is supported, but the PUCCH resources otherthan PUCCH resource 1 may be explicitly signaled. In this case, implicitsignaling for at least one ACK/NACK bit may be supported.

Supporting LTE fallback means that the following conditions described as(1) to (3) are satisfied simultaneously. In a certain PUCCH resource,one bit satisfies A:N=0:1 (=0:2=0:3) and the remaining two bitscorrespond to the mapping illustrated in FIG. 6B (1). The remaining twobits in (1) are associated with two CWs processed by PDSCH in PCell (2).The PUCCH resource in which the condition (1) is satisfied is a PUCCHresource assigned in association in a one-to-one correspondence with thetop CCE index (n_CCE) of the CCEs occupied by the PDCCH indicating thePDSCH in PCell (i.e., PUCCH resource 1 in the example illustrated inFIG. 17) (3).

It should be noted that, the mapping in FIG. 17A is an example, and themapping in which bit b0 and bit b1 are switched may be used, forexample, since the mapping only needs to satisfy the conditions (1) to(3) simultaneously. In addition, the mapping for the PUCCH resourcesother than PUCCH resource 1 supporting LTE fallback may be rotated by 90degrees, 180 degrees, and 270 degrees in the clockwise direction,respectively, for example.

As described above, it is possible to support implicit signaling foroptional response signals and LTE fallback (fallback to Format 1b inFIG. 17, to be more specific) from two CCs while improving thecharacteristics of response signals having poor transmissioncharacteristics by smoothing out, among the bits, the number of PUCCHresources each allowing the ACK/NACK to be determined only bydetermining the PUCCH resource in which the response signals arereported.

(Control Example 3: Single-CW Processing for PCell, Two-CW Processingfor SCell, and Cross-Carrier Scheduling from PCell to SCell (Part 1))

FIG. 19 illustrates a method of determining the A/N resource (i.e.,PUCCH resource) when PCell performs two-CW processing and SCell performssingle-CW processing and cross-carrier scheduling is applied when thenumber of CCs is two. FIG. 19 illustrates an example of cross-carrierscheduling from PCell to SCell, however. In other words, the PDCCH inPCell indicates the PDSCH in SCell.

In FIG. 19, PUCCH resource 1 is assigned in association in a one-to-onecorrespondence with the top CCE index (n_CCE) of the CCEs occupied bythe PDCCH indicating the PDSCH in PCell (implicit signaling).

In FIG. 19, PUCCH resource 2 in an uplink component carrier is assignedin association in a one-to-one correspondence with the top CCE index(n_CCE′) of the CCEs occupied by the PDCCH in PCell that indicates thePDSCH in SCell (implicit signaling). PUCCH resource 2 is cross-carrierscheduled from PCell to SCell. In addition, PUCCH resource 3 in anuplink component carrier is assigned in association in a one-to-onecorrespondence with the CCE index subsequent to the top CCE index(n_CCE′+1) of the CCEs occupied by the PDCCH indicating the PDSCH inSCell (implicit signaling) in FIG. 19.

It should be noted that, when cross-carrier scheduling is configuredfrom first SCell to second SCell, PUCCH resources 2 and 3 describedabove may be previously reported by the base station (explicitsignaling). In addition, when no cross-carrier scheduling is configured,PUCCH resources 2 and 3 may be previously reported by the base station,likewise (explicit signaling).

It should be noted that, the PUCCH resources except for PUCCH resource 1associated in a one-to-one correspondence with the CCE index (n_CCE) ofthe CCEs occupied by the PDCCH indicating the PDSCH in PCell (i.e.,PUCCH resources 2 and 3) may be previously reported from the basestation (explicit signaling).

FIGS. 21 and 22 illustrate the method of generating (mapping) ACK/NACKsignals when PCell performs single-CW processing and SCell performstwo-CW processing when the number of CCs is two. PUCCH resources 1, 2and 3 in FIGS. 20 and 21 correspond to PUCCH resources 1, 2 and 3illustrated in FIG. 19, respectively. The bits forming a combination ofa plurality of an ACK and/or NACK and/or DTX are termed as bits b0, b1and b2 in sequence. In addition, bits b0, b1 and b2 are respectivelyassociated with ACK/NACK signals of CW0 of the PDSCH in SCell, ACK/NACKsignals of CW1 of the PDSCH in SCell and ACK/NACK signals of CW0 of thePDSCH in PCell. The associations between the bits and ACK/NACK signalsare by no means limited to the abovementioned example.

In control example 3, in order to use the same mapping as that ofcontrol example 2 in which PCell performs two-CW processing and SCellperforms single-CW processing, bit b0 and bit b1 are associated with theCell that performs two-CW processing (or in which Space DivisionMultiplexing (SDM) is configured), and bit b2 is associated with theCell that performs single-CW (or in which no SDM is configured). Sincethe same mapping table is used, the mapping table in FIG. 20A (ormapping table in FIG. 17A) can support fallback to Format 1a and Format1b. Since the same mapping table is used, a single mapping table cansimultaneously support two control examples (i.e., the example in whichPCell performs two-CW processing and SCell performs single-CW processingand the example in which PCell performs single-CW processing and SCellperforms two-CW processing). Accordingly, the number of combinations ofmapping tables held by terminals and base stations can be less, andalso, the complexity of the configurations to transmit response signalsin terminals and also to determine the response signals in base stationscan be reduced. It should be noted that, it is not necessary to use thesame mapping always, although the additional effects obtained by usingthe same mapping table are described herein.

The response signals for all the PUCCH resources are mapped to threephase points excluding the pattern of the results of error detectionindicating a DTX in PUCCH resource 1 illustrated in FIG. 20A. Inaddition, the response signals are mapped to three phase pointsregardless of any pattern for results of error detection indicating aDTX in PUCCH resource 2 illustrated in FIG. 20A. The response signalsare mapped to two phase points in PUCCH resource 3 illustrated in FIG.20A. In addition, the response signals are mapped to the phase point foreach of the PUCCH resources in a way that makes the Hamming distancebetween adjacent phase points smaller (i.e., in a way that makes themapping closer to the Gray mapping).

FIG. 20B illustrates concentration of ACK/NACKs for PUCCH resources 1, 2and 3 for bits b0, b1 and b2 in FIG. 20A.

As described above, base stations use the two methods of determiningresponse signals depending on the mapping methods. More specifically,base station uses the method of determining the PUCCH resource in whichthe response signals are reported (determination method 1) and themethod of determining the PUCCH resource in which the response signalsare reported and further determining the phase point of the PUCCHresource (determination method 2).

FIG. 20 illustrate the mapping method that smooths out, among the bits,the number of PUCCH resources each allowing the ACK/NACK to bedetermined using determination method 1 and that supports implicitsignaling for an optional ACK/NACK bit and LTE fallback (i.e., fallbackto Format 1a in FIG. 20). This mapping method is disclosed inEmbodiment 1. FIG. 21 illustrates an ACK/NACK mapping table(transmission rule table) corresponding to FIG. 20.

The PUCCH resource allowing the ACK/NACK to be determined usingdetermination method 1 herein is the PUCCH resource corresponding to thecombination for A:N=1:0(=3:0) or A:N=0:1(=0:3=0:2) in FIG. 20B. Inaddition, the number of PUCCH resources each allowing the ACK/NACK to bedetermined is “the number of combinations for A:N=1:0 or 0:1” in FIG.20B. Moreover, the smoothing out means to perform mapping that makes thedifference between the maximum and minimum values of “the number ofcombinations for A:N=1:0 or 0:1” not greater than one. Morespecifically, in the mapping illustrated in FIG. 20, “the number ofcombinations for A:N=1:0 or 0:1” is two for one bit (i.e., b2) and onefor the remaining two bits (i.e., b0 and b1) in a case where PCellperforms single-CW processing and SCell performs two-CW processing whenthe two CC are used. Accordingly, the difference between the maximum andminimum values is one in this mapping.

In other words, supporting implicit signaling for an optional ACK/NACKbit means that bit b2 associated with ACK/NACK of CW0 of PCell takes noDTX for mapping in PUCCH resource 1 associated with the top CCE index(n_CCE) of the CCEs occupied by the PDCCH indicating the PDSCH in PCellin FIG. 20A. Likewise, supporting implicit signaling for an optionalACK/NACK bit means that the bit b0 takes no DTX for mapping in PUCCHresource 1, and the bit b1 takes no DTX for mapping in PUCCH resource 2.

It should be noted that, FIG. 20 illustrate an example in which all thePUCCH resources are implicitly signaled, so that implicit signaling foran optional ACK/NACK bit is supported, but the PUCCH resources otherthan PUCCH resource 3 may be explicitly signaled. In this case, implicitsignaling for at least one ACK/NACK bit may be supported.

Supporting LTE fallback means that the following conditions described as(1) to (3) are satisfied simultaneously. In a certain PUCCH resource,two bits satisfy A:N=0:1 (=0:2=0:3) and the remaining one bitcorresponds to the mapping illustrated in FIG. 6A (1). The remaining onebit in (1) is associated with single CW processed by PDSCH in PCell (2).The PUCCH resource in which the condition (1) is satisfied is a PUCCHresource assigned in association in a one-to-one correspondence with thetop CCE index (n_CCE) of the CCEs occupied by the PDCCH indicating thePDSCH in PCell (i.e., PUCCH resource 3 in the example illustrated inFIG. 20) (3).

It should be noted that, the mapping in FIG. 20A is an example, and themapping in which bit b0 and bit b1 are switched may be used, forexample, since the mapping only needs to satisfy the conditions (1) to(3) simultaneously. In addition, the mapping for the PUCCH resourcesother than PUCCH resource 3 supporting LTE fallback may be rotated by 90degrees, 180 degrees, and 270 degrees in the clockwise direction,respectively, for example.

As described above, it is possible to support implicit signaling foroptional response signals and LTE fallback (fallback to Format 1a inFIG. 20, to be more specific) from two CCs while improving thecharacteristics of response signals having poor transmissioncharacteristics by smoothing out, among the bits, the number of PUCCHresources each allowing the ACK/NACK to be determined only bydetermining the PUCCH resource in which the response signals arereported.

Control Example 4: Single-CW Processing for PCell, Two-CW Processing forSCell, and Cross-Carrier Scheduling from PCell to SCell

Control example 4 has many parts in common with control example 3. Thus,the description of common parts will be omitted.

FIGS. 22 and 23 illustrate a method of generating (mapping) ACK/NACKsignals when PCell performs single-CW processing and SCell performstwo-CW processing. PUCCH resources 1, 2 and 3 in FIGS. 22 and 23correspond to PUCCH resources 1, 2 and 3 illustrated in FIG. 19,respectively. The bits forming a combination of a plurality of an ACKand/or NACK and/or DTX are termed as bits b0, b1 and b2 in sequence. Inaddition, bits b0, b1 and b2 are respectively associated with ACK/NACKsignals of CW0 of the PDSCH in SCell, ACK/NACK signals of CW1 of thePDSCH in SCell and ACK/NACK signals of CW0 of the PDSCH in PCell. Theassociations between the bits and ACK/NACK signals are by no meanslimited to the abovementioned example.

In control example 4, it is possible to use the same mapping as thatused in the case where PCell performs two-CW processing and SCellperforms single-CW processing. When the same mapping is used, onlyfallback to Format 1a can be supported, and fallback to Format 1b cannotbe supported. The use of the same mapping makes it possible tosimultaneously support two control examples (i.e., the example in whichPCell performs two-CW processing and SCell performs single-CW processingand the example in which PCell performs single-CW processing and SCellperforms two-CW processing). Accordingly, the number of combinations ofmapping tables held by terminals and base stations can be less, andalso, the complexity of the configuration to transmit response signalsin terminals and also to determine the response signals in base stationscan be reduced. Meanwhile, when different mapping is used, fallback toFormat 1a can be supported in FIG. 22. Support for fallback to Format 1bis dependent of the mapping used when PCell performs two-CW processingand SCell performs single-CW processing. It should be noted that, it isnot necessary to use the same mapping always, although the additionaleffects obtained by using the same or different mapping table aredescribed herein.

The response signals are mapped to two phase points regardless of anypattern for results of error detection indicating a DTX in PUCCHresource 1 illustrated in FIG. 22A. The response signals are mapped tofour phase points regardless of any pattern for results of errordetection indicating a DTX in PUCCH resource 2 illustrated in FIG. 22A.The response signals are mapped to two phase points regardless of anypattern for results of error detection indicating a DTX in PUCCHresource 3 illustrated in FIG. 22A. In addition, the response signalsare mapped to the phase point for each of the PUCCH resources in a waythat makes the Hamming distance between adjacent phase points smaller(i.e., in a way that makes the mapping closer to the Gray mapping).

FIG. 22B illustrates concentration of ACK/NACKs of PUCCH resources 1, 2and 3 for bits b0, b1 and b2 in FIG. 22A.

FIG. 22 illustrate the mapping method that smooths out, among the bits,the number of PUCCH resources each allowing the ACK/NACK to bedetermined using determination method 1 and that supports implicitsignaling for an optional ACK/NACK bit and LTE fallback (i.e., fallbackto Format 1a in FIG. 22). This mapping method is disclosed inEmbodiment 1. FIG. 23 illustrates an ACK/NACK mapping table(transmission rule table) corresponding to FIG. 22.

As described above, it is possible to support implicit signaling foroptional response signals and LTE fallback (fallback to Format 1a inFIG. 22, to be more specific) from two CCs while improving thecharacteristics of response signals having poor transmissioncharacteristics by smoothing out, among the bits, the number of PUCCHresources each allowing the ACK/NACK to be determined only bydetermining the PUCCH resource in which the response signals arereported.

Control Example 5: Control Example with Mapping Table with Applicationof RANK Adaptation

Control example 5 discloses mapping tables used in case of control thatswitches between the mapping tables not only according to the number ofconfigured component carriers (CC) and the transmission mode, but alsodynamically controlled Rank Adaptation. More specifically, controlexample 5 discloses the mapping tables used in a case where the numberof CWs configured in PCell or SCell (e.g., two CWs on PCell and two CWson SCell) is decreased (e.g., two CWs on PCell and single CW on SCell)because of Rank Adaptation. In other words, the resource for ACK/NACK tobe reported to an eNB and the constellation position in the resource aredetermined not according to the mapping table based on the number ofACK/NACK bits found from the number of configured CWs, but according tothe mapping table based on the number of ACK/NACK bits found from thenumber of CWs after rank adaptation.

For example, when one PCell and one SCell are each configured with twoCWs while the SCell transmits only a single CW to a UE because of rankadaptation, the number of ACK/NACKs to be reported from the UE to theeNB can be three instead of the number of configured CWs, which is four.In this case, the terminal may report ACK/NACKs to the eNB using amapping table for three bits (i.e., table 1(b)).

In this case, however, when the UE receives a single CW of the PDCCHfrom SCell, but fails to receive the PDCCH from PCell, for example, theACK/NACK bit corresponding to the data on PCell results in a DTX. TheUE, however, cannot determine whether the data on PCell is a single CWor two CWs because of the failure to receive the PDCCH. For this reason,the UE cannot determine whether to use the mapping table for three bits(i.e., two CWs for PCell and single CW for SCell) or the mapping tablefor two bits (i.e., single CW for PCell and single CW for SCell).According to the claimed invention, a DTX can be correctly reported tothe eNB even in such a case.

A description will be provided with reference to FIGS. 24 to 26,hereinafter. It is to be noted that, the mapping table disclosed in FIG.24 has the characteristics described in control example 4, the mappingtable disclosed in FIG. 25 has the characteristics described in controlexamples 2 and 3, and the mapping table disclosed in FIG. 26 has thecharacteristics described in control example 1, so that the detaileddescription of the mapping tables will be omitted. In other words, themapping tables disclosed in FIGS. 24 to 26 support LTE fallback from twoCCs while improving the characteristics of response signals having poortransmission characteristics by smoothing out the number of PUCCHresources each allowing the ACK/NACK to be determined only bydetermining the PUCCH resource in which the response signals arereported.

A description will be provided with reference to FIGS. 24 and 25. ThePUCCH resource and the constellation position in the resource when PCell(i.e., SDM Cell) is DTX (DTX, DTX) and SCell (Non-SDM Cell) is ACK inthe three-bit mapping table in FIG. 25 coincide with the PUCCH resourceand the constellation position in the resource when PCell is DTX andSCell is ACK in the two-bit mapping table in FIG. 25. Likewise, whenSCell is ACK, the PUCCH resource and the constellation point in theresource correspond to No transmission in both of the tables. In a casewhere PCell is single-CW transmission and SCell is a DTX (i.e., UEcannot determine whether it is single-CW transmission or two-CWtransmission), the PUCCH resources and the constellation positions inthe resources in the two-bit mapping table and three-bit mapping tablecoincide with each other because the mapping tables illustrated in FIGS.24 and 25 both support PUCCH format 1a.

A description will be provided with reference to FIGS. 25 and 26,likewise. The PUCCH resource and the constellation position in theresource when PCell is DTX (DTX, DTX) and SCell is (ACK, ACK) in thefour-bit mapping table in FIG. 26 coincide with the PUCCH resource andthe constellation position in the resource when PCell (i.e., non-SDMCell) is DTX and SCell is (ACK, ACK) in the three-bit mapping table inFIG. 25. Likewise, when SCell is NACK, the PUCCH resource corresponds toNo transmission in both of the tables. In a case where PCell performstwo-CW transmission and SCell results in a DTX (i.e., UE cannotdetermine whether it is single-CW transmission or two-CW transmission),the PUCCH resources and the constellation positions in the resources ofthe three-bit mapping table and four-bit mapping table coincide witheach other because the mapping tables illustrate in FIGS. 25 and 26 bothsupport PUCCH format 1b.

The method of determining the A/N resource used for transmission ofresponse signals and the method of generating ACK/NACK signals have beendescribed using control examples 1 to 5.

As described above, terminal 200 controls transmission of responsesignals by selecting the resource used for the transmission of responsesignals from a PUCCH resource associated with a CCE and a specific PUCCHresource previously reported by base station 100 in case of channelselection. Terminal 200 can support implicit signaling for optionalresponse signals and LTE fallback from two CCs while improving thecharacteristics of response signals having poor transmissioncharacteristics by smoothing out, among the bits, the number of PUCCHresources each allowing the ACK/NACK to be determined only bydetermining the PUCCH resource in which the response signals arereported.

Moreover, base station 100 selects the resource used for transmission ofthe response signals, from the PUCCH resource associated with the CCEand the specific resource previously reported to terminal 200. Basestation 100 determines the ACK/NACK using the mapping that smooths out,among the bits, the number of PUCCH resources each allowing the ACK/NACKto be determined only by determining the PUCCH resource used forreporting the response signals.

Thus, according to Embodiment 1, it is possible to support LTE fallbackfrom two CCs while improving the characteristics of response signalshaving poor transmission characteristics by smoothing out, among thebits, the number of PUCCH resources each allowing the ACK/NACK to bedetermined only by determining the PUCCH resource in which the responsesignals are reported in a case where ARQ is applied to communicationsusing an uplink component carrier and a plurality of downlink componentcarriers associated with the uplink component carrier while CCEs in aPDCCH region in PCell are associated in a one-to-one correspondence withPUCCH resources in the uplink component carrier.

Embodiment 2

In Embodiment 2, a description will be provided regarding a case wherethe combination of the PUCCH resource associated in a one-to-onecorrespondence with the top CCE index of the CCEs occupied by the PDCCHindicating the assignment of PDSCH in PCell (i.e., PUCCH resource to beimplicitly signaled) and the bit (ACK/NACK bit) representing a result oferror detection on a CW received on PCell is switched according to thenumber of component carriers and the transmission mode configured forthe terminal.

It should be noted that, the transmission mode supporting only single-CWtransmissions is referred to as “non-MIMO (Multiple Input MultipleOutput) mode” and the transmission mode supporting up to two-CWtransmissions is referred to as “MIMO mode.”

As in the case of Embodiment 1, terminals generate response signals tobe fed back to base stations on the basis of an association (i.e.,ACK/NACK mapping table or transmission rule table for response signals)among a pattern candidate of results of error detection (may be referredto as “error detection result pattern” or “ACK/NACK state,”hereinafter), a PUCCH resource to which the response signals areassigned, and the phase point in the PUCCH resource. It should be notedthat, the error detection result pattern consists of results of errordetection on a plurality of pieces of downlink data received on at leasttwo downlink component carriers.

The ACK/NACK mapping table is determined according to the number ofdownlink component carriers previously configured for the terminal(i.e., at least two downlink component carriers since carrieraggregation is performed) and the transmission mode. To put it morespecifically, the ACK/NACK mapping table is determined according to thenumber of ACK/NACK bits specified by the number of downlink componentcarriers and the transmission mode.

FIG. 27 illustrate examples of mapping for error detection resultpatterns in a case where the number of downlink component carriersconfigured for the terminal is two (one PCell and one SCell).

FIG. 27A illustrates an example of mapping when the non-MIMO mode isconfigured in each of the downlink component carriers. In other words,FIG. 27A illustrates an example of mapping when the error detectionresult pattern (i.e., the number of ACK/NACK bits) is represented by twobits (i.e., mapping for two bits). FIG. 27B illustrates an example ofmapping when the non-MIMO mode is configured in one of the downlinkcomponent carriers and the MIMO mode is configured in the other downlinkcomponent carrier. In other words, FIG. 27B illustrates an example ofmapping when the error detection result pattern (i.e., the number ofACK/NACK bits) is represented by three bits (i.e., mapping for threebits). FIG. 27C illustrates an example of mapping when the MIMO mode isconfigured in each of the downlink component carriers. In short, FIG.27C illustrates an example of mapping when the error detection resultpattern (i.e., the number of ACK/NACK bits) is represented by four bits(i.e., mapping for four bits).

The mapping tables illustrated in FIGS. 28A to C correspond to theexamples of mapping illustrated in FIGS. 27A to C, respectively.

As illustrated in FIGS. 27A to C and FIGS. 28A to C, the error detectionresult pattern is represented by a maximum of four bits (i.e., b0 tob3). In addition, as illustrated in FIGS. 27A to C and FIGS. 28A to C, amaximum of four PUCCH resources 1 to 4 (i.e., Ch1 to Ch4) is configured.

For example, a description will be provided regarding a case where theMIMO mode is configured in PCell and the non-MIMO mode is configured inSCell in FIG. 27B (FIG. 28). For example, as illustrated in FIG. 27B,the response signals are mapped to the symbol position (i.e., phasepoint) (−1, 0) of PUCCH resource 1 when b0 of the result of errordetection on CW0 of PCell is an ACK and b1 of the result of errordetection on CW1 of PCell is an ACK, and b2 of the result of errordetection on CW0 of SCell is a NACK or DTX. PUCCH resource 1 illustratedin FIG. 27B is the PUCCH resource associated in a one-to-onecorrespondence with the top CCE index of the CCEs occupied by the PDCCHindicating the assignment of PDSCH in PCell.

As described above, when the number of bits forming the error detectionresult pattern (i.e., the number of ACK/NACK bits) is not greater thanfour, the terminal feeds back the response signals using channelselection or DFT-S-OFDM. Whether to use channel selection or DFT-S-OFDMis previously configured by the base station. On the other hand, whenthe number of bits forming the error detection result pattern (i.e., thenumber of ACK/NACK bits) is greater than four, the terminal feeds backthe response signals using DFT-S-OFDM.

LTE-Advanced defines mapping for error detection result patterns used inchannel selection that is optimized for a case where the number ofdownlink component carriers is two, assuming the introductory phase ofthe service (e.g., FIGS. 27 and 28).

The mapping optimized for a case where the number of downlink componentcarriers is two herein is mapping that can be switched to and used asthe mapping for the error detection result pattern for one CC used inthe LTE system (i.e., mapping that supports LTE fallback). Morespecifically, in the mapping that supports LTE fallback, as illustratedin FIG. 28C, for example, the phase points in PUCCH resource 1associated with specific error detection result patterns in which b2 andb3 of the results of error detection on CWs received in SCell become allDTXes are identical with the phase points associated with the results oferror detection identical with b0 and b1 of the results of errordetection on CWs received in PCell in the specific error detectionresult patterns in another ACK/NACK mapping table used when the numberof CCs is one (e.g., FIG. 6B). The same applies to FIGS. 28A and B.

Accordingly, even when the understanding about number of CCs configuredfor a terminal is different between a base station and the terminal, thebase station can correctly determine the response signals for PCell andSCell.

However, LTE-Advanced may support three or four downlink componentcarriers in the future. In this case, mapping supporting three or fourdownlink component carriers while reusing the mapping optimized for acase where the number of downlink component carriers is two ispreferably used in terms of simplification of the configurations ofterminals and base stations.

In this regard, implicitly signaling the PUCCH resources for a maximumnumber of CWs supported in PCell in dynamic scheduling has been proposed(see, “Panasonic, 3GPP RAN1 meeting #63bis, R1-110192, “Text Proposalfor PUCCH Resource Allocation for channel selection,” January 2011”).For example, when the MIMO mode is configured in PCell (in case oftransmission of a maximum of two CWs), two PUCCH resources areimplicitly signaled. In this case, one of the two implicitly signaledPUCCH resources is associated in a one-to-one correspondence with thetop CCE index of the CCEs occupied by the PDCCH indicating theassignment of PDSCH in PCell. In addition, the other implicitly signaledPUCCH resource is associated in a one-to-one correspondence with thesecond CCE index subsequent to the top CCE index of the CCEs occupied bythe PDCCH indicating the assignment of PDSCH in PCell.

Meanwhile, when the non-MIMO mode is configured in PCell, one PUCCHresource is implicitly signaled. The PUCCH resource is associated in aone-to-one correspondence with the top CCE index of the CCEs occupied bythe PDCCH indicating the assignment of PDSCH in PCell.

For example, in FIGS. 27C and 28C, the MIMO mode is configured in PCell.Accordingly, PUCCH resource 1 (Ch1) and PUCCH resource 2 (Ch2) areimplicitly signaled in FIGS. 27C and 28C. Meanwhile, PUCCH resource 3(Ch3) and PUCCH resource 4 (Ch4) are explicitly signaled in FIGS. 27Cand 28C.

In addition, an assumption is made that the MIMO mode is configured inPCell while the non-MIMO mode is configured in SCell in FIGS. 27B and28B. In this case, PUCCH resource 1 (Ch1) and PUCCH resource 2 (Ch2) areimplicitly signaled and PUCCH resource 3 (Ch3) is explicitly signaled inFIGS. 27B and 28B.

Alternatively, an assumption is made that the non-MIMO mode isconfigured in PCell and the MIMO mode is configured in SCell in FIGS.27B and 28B. In this case, PUCCH resource 3 (Ch3) is implicitly signaledand PUCCH resource 1 (Ch1) and PUCCH resource 2 (Ch2) are explicitlysignaled in FIGS. 27B and 28B.

Moreover, the non-MIMO mode is configured in PCell and SCell in FIGS.27A and 28A. In this case, PUCCH resource 1 (Ch1) is implicitly signaledand PUCCH resource 2 (Ch2) is explicitly signaled in FIGS. 27A and 28A.

As described above, when the number of bits of an error detection resultpattern is not greater than four, the terminal can feed back theresponse signals using channel selection. FIG. 29 illustrates the numberof CWs on PCell, the numbers of CWs on SCells (i.e., SCells 1 to 3) andthe number of ACK/NACK signals (the number of ACK/NACK bits representingan error detection result pattern) used for feedback of response signalsusing channel selection in a case where the numbers of downlinkcomponent carriers are two (two CCs), three (three CCs) and four (fourCCs).

For example, in FIG. 29, the number of ACK/NACK bits is three when thenumber of downlink component carriers is three and the non-MIMO mode isconfigured in each of PCell, SCell 1 and SCell 2. Accordingly, theterminal uses the mapping for three bits (ACK/NACK mapping table)illustrated in FIGS. 27B and 28B.

Meanwhile, the number of ACK/NACK bits is four when the number ofdownlink component carriers is three (three CCs) and the MIMO mode isconfigured in one of PCell, SCell 1 and SCell 2 and the non-MIMO mode isconfigured in each of the other two Cells in FIG. 29. Accordingly, theterminal uses the mapping for four bits (i.e., ACK/NACK mapping table)illustrated in FIGS. 27C and 28C.

The number of ACK/NACK bits is four in a case where the number ofdownlink component carriers is four (four CCs) and the non-MIMO mode isconfigured in each of PCell and SCells 1 to 3 in FIG. 29. Accordingly,the terminal uses the mapping for four bits (i.e., ACK/NACK mappingtable) illustrated in FIGS. 27C and 28C.

However, when the number of bits of an error detection result pattern isnot greater than four, while the number of downlink component carriersis three or four and the non-MIMO mode is configured in PCell, all thePUCCH resources need to be explicitly signaled (see, “LG Electronics,3GPP RAN1 meeting #63, R1-106129, “PUCCH resource allocation forACK/NACK,” November 2010,” for example). In other words, implicitsignaling cannot be used in a case where the number of bits of an errordetection result pattern is not greater than four, while the number ofdownlink component carriers is three or four and the non-MIMO mode isconfigured in PCell.

Hereinafter, a description will be provided regarding the reasons whyimplicit signaling cannot be used when the number of bits of an errordetection result pattern is not greater than four, while the number ofdownlink component carriers is three or four and the non-MIMO mode isconfigured in PCell. As an example, a description will be providedregarding a case where the four downlink component carriers includingPCell and SCells 1 to 3 are configured for one terminal and the non-MIMOmode is configured in each of the downlink component carriers asillustrated in FIG. 30 (i.e., same ACK/NACK mapping table as that inFIG. 28C). More specifically, as illustrated in FIG. 30, the results oferror detection on PCell, SCell 1, SCell 2 and SCell 3 are representedby four bits, which are b0, b1, b2 and b3, respectively.

As described above, according to the method in which the PUCCH resourcesfor the maximum number of CWs supported by PCell are implicitlysignaled, PUCCH resource 1 (Ch1) is implicitly signaled and PUCCHresources 2 to 4 (Ch2 to Ch4) are explicit signaled. To put itdifferently, PUCCH resource 1 (Ch1) is associated in a one-to-onecorrespondence with the top CCE index of the CCEs occupied by the PDCCHindicating the assignment of the PDSCH in PCell.

As illustrated in FIG. 30, the ACK/NACK states (b0, b1, b2 and b3)=(D,A, N/D, and N/D) are mapped to the phase point “−j” of PUCCH resource 1(Ch1). However, the result of error detection result on PCell, b0, isDTX, which means that the terminal has failed to receive the PDCCHintended for the terminal in PCell. For this reason, the terminal cannotidentify the position of PUCCH resource 1 (CH1) in this case.

Accordingly, in FIG. 30, when PUCCH resource 1 (Ch1) is implicitlysignaled, the terminal cannot feedback the ACK/NACK states (b0, b1, b2and b3)=(D, A, N/D, N/D) to the base station. For this reason, when theACK/NACK states (b0, b1, b2 and b3)=(D, A, N/D, N/D), the terminalcannot feedback an ACK to the base station even though the result oferror detection on SCell, b1, is an ACK. Accordingly, the base stationperforms unnecessary retransmission processing for SCell 1 although theresult of error detection on SCell, b1, is an ACK.

Because of the reasons mentioned above, when the number of bits of anerror detection result pattern is not greater than four, while thenumber of downlink component carriers is three or four and non-MIMO isconfigured in PCell, all PUCCH resources 1 to 4 (Ch1 to Ch4) need to beexplicitly signaled.

Meanwhile, when the number of bits of an error detection result patternis four while the number of downlink component carriers is two, PUCCHresources 1 and 2 (Ch1 and Ch2) are implicitly signaled using a singlePDCCH in PCell. More specifically, when receiving the abovementionedPDCCH normally, the terminal can identify both of PUCCH resources 1 and2 (Ch1 and Ch2). However, when failing to receive the abovementionedPDCCH, the terminal cannot identify neither PUCCH resource 1 nor 2 (Ch1nor Ch2). To put it differently, no such situation where “DTX, ACK”occurs as the results of error detection on two CWs received in PCell.More specifically, when the number of downlink component carriers istwo, the results of error detection would not be the ACK/NACK states(b0, b1, b2 and b3)=(D, A, N/D, N/D) in FIG. 28C. Accordingly, such asituation where the implicitly signaled PUCCH resource cannot be useddoes not occur when the number of downlink component carriers is two.

Likewise, when the number of bits of an error detection result patternis three, while the number of downlink component carriers is two and thenon-MIMO mode is configured in PCell, PUCCH resource 3 (Ch3) isimplicitly signaled using the PDCCH in PCell as illustrated in FIG. 19,for example. As illustrated in FIG. 28B, in this case, PUCCH resource 3(Ch3) is used when the result of error detection on the CW received inPCell is an ACK or NACK. To put it differently, as illustrated in FIG.28B, when PUCCH resource 3 (Ch3) is used, the terminal is in a statewhere the terminal has received the PDCCH normally. Accordingly, in thiscase as well, no such situation where the implicitly signaled PUCCHresource cannot be used as described above occurs.

Meanwhile, if all PUCCH resources 1 to 4 (Ch1 to Ch4) are explicitlysignaled when the number of bits of an error detection result pattern isnot greater than four while the number of downlink component carriers isthree or four, the overhead of the PUCCH resources is increased.

Meanwhile, the PUCCH resources to be implicitly signaled are associatedin a one-to-one correspondence with the CCEs (i.e., CCE index) occupiedby the PDCCH indicating the assignment of the PDSCH. For this reason,the PUCCH resources occupy the PUCCH resource region in size defineddepending on the CCE index. In contrast to such a PUCCH resource, thePUCCH resource to be explicitly signaled occupies a PUCCH resourceregion configured additionally and separately from the resource to beimplicitly signaled.

Meanwhile, the PUCCH resource to be explicitly signaled preferablyoccupies a PUCCH resource region different from a PUCCH resource regionoccupied by the PUCCH resource to be implicitly signaled. This isbecause, when PUCCH resources to be implicitly signaled and PUCCHresources to be explicitly signaled are shared, and if a certainterminal uses a shared resource as an explicitly signaled PUCCHresource, the shared PUCCH resource cannot be used in the terminal andother terminals as a PUCCH resource to be implicitly signaled inconsideration of a possible collision with the shared PUCCH resource. Asdescribed, sharing implicitly signaled PUCCH resources and explicitlysignaled PUCCH resources provides restrictions on scheduling in basestations.

When explicitly signaled PUCCH resources and implicitly signaled PUCCHresources are not shared, the explicitly signaled PUCCH resources areconfigured separately from the implicitly signaled PUCCH resources.Accordingly, as the number of the PUCCH resources to be explicitlysignaled among the PUCCH resources used for feeding back responsesignals is increased, the amount of overhead of the PUCCH is increased.

As described above, when the number of bits of an error detection resultpattern is not greater than four, while the number of downlink componentcarriers is three or four and the non-MIMO mode is configured in PCell,there may be a situation where the implicitly signaled PUCCH resource inPCell cannot be identified, so that unnecessary retransmission isperformed. Meanwhile, if explicitly signaled PUCCH resources are usedalone, the overhead of the PUCCH becomes larger.

In this respect, when the number of bits of an error detection resultpattern is not greater than four while the number of downlink componentcarriers is three or four, the terminal switches the combination of thePUCCH resource to be implicitly signaled and an ACK/NACK bitrepresenting the result of error detection on an CW received in PCell,on the basis of the transmission mode configured in PCell and theACK/NACK mapping table.

(Operations of Base Station 100 and Terminal 200)

A description will be provided regarding operations of base station 100(FIG. 10) and terminal 200 (FIG. 11) according to Embodiment 2.

Hereinafter, a description will be provided regarding a case where thenumber of downlink component carriers is not greater than four while thenumber of bits (i.e., number of ACK/NACK bits) forming an errordetection result pattern is equal to or greater than the number ofdownlink component carriers but not greater than four.

Hereinafter, a description will be provided regarding cases 1 to 8 inwhich the number of downlink component carriers, the number of ACK/NACKbits and the transmission mode configured in PCell are different.

(Case 1: Where Number of Downlink Component Carriers is Two and Numberof ACK/NACK Bits is Four)

More specifically, in case 1, the MIMO mode is configured in each ofPCell and SCell.

In case 1, terminals 200 use mapping for four bits (i.e., ACK/NACKmapping table) illustrated in FIG. 27C and FIG. 28C. In FIG. 28C, bitsb0 and b1 respectively represent the results of error detection on twoCWs received in PCell and bits b2 and b3 respectively represent theresults of error detection on two CWs received in SCell.

In addition, in case 1, the PUCCH resources for the maximum number ofCWs supported in PCell in dynamic scheduling are implicitly signaled.Accordingly, since the MIMO mode is configured in PCell in case 1, twoPUCCH resources are implicitly signaled.

For example, in FIG. 27C and FIG. 28C, PUCCH resource 1 (Ch1) and PUCCHresource 2 (Ch2) are implicitly signaled and PUCCH resource 3 (Ch3) andPUCCH resource 4 (Ch4) are explicitly signaled.

In case 1, base station 100 notifies terminals 200 of four PUCCHresources 1 to 4 (Ch1 to Ch4) as described above.

(Case 2: Where Number of Downlink Component Carriers is Two, Number ofACK/NACK Bits is Three and MIMO Transmission Mode is Configured inPCell)

More specifically, the MIMO mode is configured in PCell and the non-MIMOmode is configured in SCell in case 2.

In case 1, terminals 200 use mapping for three bits (i.e., ACK/NACKmapping table) illustrated in FIG. 27B and FIG. 28B. In FIG. 28B, bitsb0 and b1 respectively represent the results of error detection on twoCWs received in PCell and bit b2 represents the result of errordetection on single CW received in SCell.

In addition, in case 2, the PUCCH resources for the maximum number ofCWs supported in PCell in dynamic scheduling are implicitly signaled.Accordingly, since the MIMO mode is configured in PCell in case 2, twoPUCCH resources are implicitly signaled.

For example, in FIG. 27B and FIG. 28B, PUCCH resource 1 (Ch1) and PUCCHresource 2 (Ch2) are implicitly signaled and PUCCH resource 3 (Ch3) isexplicitly signaled.

In case 2, base station 100 notifies terminals 200 of three PUCCHresources 1 to 3 (Ch1 to Ch3) as described above.

(Case 3: Where Number of Downlink Component Carriers is Two, Number ofACK/NACK Bits is Three and Non-MIMO Transmission Mode is Configured inPCell)

More specifically, the non-MIMO mode is configured in PCell and the MIMOmode is configured in SCell in case 3.

In case 3, terminals 200 use mapping for three bits (i.e., ACK/NACKmapping table) illustrated in FIG. 27B and FIG. 28B. In FIG. 28B, bitsb0 and b1 respectively represent the results of error detection on twoCWs received in SCell and bit b2 represents the result of errordetection on single CW received in PCell.

In addition, in case 3, the PUCCH resources for the maximum number ofCWs supported in PCell in dynamic scheduling are implicitly signaled.Accordingly, since the non-MIMO mode is configured in PCell in case 3,one PUCCH resource is implicitly signaled.

For example, in FIG. 27B and FIG. 28B, PUCCH resource 3 (Ch3) isimplicitly signaled and PUCCH resource 1 (Ch1) and PUCCH resource 2(Ch2) are explicitly signaled.

In case 3, base station 100 notifies terminals 200 of three PUCCHresources 1 to 3 (Ch1 to Ch3) as described above.

(Case 4: Where Number of Downlink Component Carriers is Two and Numberof ACK/NACK Bits is Two)

More specifically, the non-MIMO mode is configured in each of PCell andSCell in case 4.

In case 4, terminals 200 use mapping for two bits (i.e., ACK/NACKmapping table) illustrated in FIG. 27A and FIG. 28A. In FIG. 28A, bit b0represents the result of error detection on single CW received in PCelland bit b1 represents the result of error detection on single CWreceived in SCell.

In addition, in case 4, the PUCCH resources for the maximum number ofCWs supported in PCell in dynamic scheduling are implicitly signaled.Accordingly, since the non-MIMO mode is configured in PCell in case 4,one PUCCH resource is implicitly signaled.

For example, in FIG. 27A and FIG. 28A, PUCCH resource 1 (Ch1) isimplicitly signaled and PUCCH resource 2 (Ch2) is explicitly signaled.

In case 4, base station 100 notifies terminals 200 of two PUCCHresources 1 and 2 (Ch1 and Ch2) as described above.

(Case 5: Where Number of Downlink Component Carriers is Three, Number ofACK/NACK Bits is Four and MIMO Transmission Mode is Configured in PCell)

More specifically, the MIMO mode is configured in PCell and the non-MIMOmode is configured in SCells 1 and 2 in case 5.

In case 5, terminals 200 use mapping for four bits (i.e., ACK/NACKmapping table) illustrated in FIG. 27C and FIG. 28C. In FIG. 28C, bitsb0 and b1 respectively represent the results of error detection on twoCWs received in PCell and bits b2 and b3 represent the results of errordetection on two CWs received in SCells 1 and 2, respectively.

In addition, in case 5, the PUCCH resources for the maximum number ofCWs supported in PCell in dynamic scheduling are implicitly signaled.Accordingly, since the MIMO mode is configured in PCell in case 5, twoPUCCH resources are implicitly signaled.

For example, in FIG. 27C and FIG. 28C, PUCCH resource 1 (Ch1) and PUCCHresource (Ch2) are implicitly signaled, and PUCCH resource 3 (Ch3) andPUCCH resource 4 (Ch4) are explicitly signaled.

In case 5, base station 100 notifies terminals 200 of four PUCCHresources 1 to 4 (Ch1 to Ch4) as described above.

(Case 6: Where Number of Downlink Component Carriers is Four and Numberof ACK/NACK Bits is Four)

More specifically, the non-MIMO mode is configured in each of PCell andSCells 1 to 3 in case 6.

FIG. 31 illustrates the method of determining the PUCCH resource inPCell and SCells 1 to 3 in the case where the number of downlinkcomponent carriers is four, for example.

In case 6, terminals 200 use mapping for four bits (i.e., ACK/NACKmapping table) illustrated in FIG. 27C and FIG. 28C. In FIG. 32A (i.e.,the same ACK/NACK mapping table as that in FIG. 28C), bit b0 representsthe result of error detection on single CW received in PCell and bits b1to b3 represent the results of error detection on three CWs received inSCells 1 to 3, respectively.

In addition, in case 6, the PUCCH resources for the maximum number ofCWs supported in PCell in dynamic scheduling are implicitly signaled.Accordingly, since the non-MIMO mode is configured in PCell in case 6,one PUCCH resource is implicitly signaled.

In case 6, the PUCCH resource to be implicitly signaled is PUCCHresource 3 (Ch3) as illustrated in FIG. 32A. In other words, in FIG.32A, the PUCCH resources to be explicitly signaled are PUCCH resources1, 2 and 4 (Chs 1, 2 and 4) in FIG. 32A.

As illustrated in FIG. 32A, the cases where PUCCH resource 3 (Ch3) isused are when the ACK/NACK states (b0, b1, b2 and b3) are (A, N/D, A andA), (A, N/D, A and N/D), (A, A, N/D and A) and (A, N/D, N/D, and A).

In FIG. 32A, a description will be provided with reference to bit “b0,”which represents the result of error detection on the CW received onPCell (i.e., result of error detection on the PDSCH inn PCell). Asillustrated in FIG. 32A, when PUCCH resource 3 (Ch3) is used, bit b0 isalways an “ACK.” More specifically, the ratio of ACK to NACK for PUCCHresource 3 (Ch3) as illustrated in FIG. 32A (A:N) is A:N=1:0(=4:0). Inother words, terminals 200 use PUCCH resource 3 (Ch3) for transmissionof the response signals only when the result of error detection on theCW received in PCell is an “ACK.”

As described above, PUCCH resource 3 (Ch3) is the PUCCH resource usedonly when terminal 200 succeeds in receiving the PDCCH intended forterminal 200 (i.e., indication to assign PDSCH) in PCell (i.e., whenb0=ACK). In other words, when terminal 200 fails to receive the PDCCHintended for terminal 200 in PCell (b0=DTX), PUCCH resource 3 (Ch3) isnot used. More specifically, as illustrated in FIG. 32A, terminal 200uses one of explicitly signaled PUCCH resources 1, 2 and 4 when failingto receive the PDCCH intended for terminal 200 in PCell (b0=DTX). To putit differently, PUCCH resource 3 (Ch3) supports implicit signaling forbit b0.

Accordingly, it is possible to prevent unnecessary retransmissionprocessing from occurring due to a situation where terminal 200 cannotidentify the position of the PUCCH resource used for transmission of theresponse signals.

As described above, in the ACK/NACK mapping table (FIG. 32A) in case 6,the PUCCH resource associated in a one-to-one correspondence with thetop CCE index of the CCEs occupied by the PDCCH indicating theassignment of PDSCH in PCell (i.e., PUCCH resource 3 in FIG. 32A) is thePUCCH resource in which the result of error detection on the CW receivedin PCell becomes only an ACK in each of the error detection resultpatterns associated with the PUCCH resource (i.e., b0 in FIG. 32A).

Alternatively, in the ACK/NACK mapping table in case 6, the PUCCHresource to be implicitly signaled may be the PUCCH resource in whichthe result of error detection on the CW received in PCell becomes only aNACK (i.e., result other than DTX) in each of the error detection resultpatterns associated with the PUCCH resource.

In addition, case 6 is compared with case 1 (i.e., case where the numberof downlink component carriers is two and the number of ACK/NACK bits isfour), for example. In case 1 (FIG. 28C), the PUCCH resource to beimplicitly signaled is PUCCH resource 1 (Ch1). On the other hand, incase 6 (FIG. 32A), the PUCCH resource to be implicitly signaled is PUCCHresource 3 (Ch3). In other words, case 6 (i.e., PCell: non-MIMO mode)and case 1 (i.e., PCell: MIMO mode) use the same number of ACK/NACK bitsand the same ACK/NACK mapping table, but use a different PUCCH resourceto be implicitly signaled.

In addition, case 6 and case 1 use a different combination of the PUCCHresource to be implicitly signaled and the bit representing the resultof error detection on the CW received in PCell (i.e., PUCCH resource 3and b0 in case 6 and PUCCH resource 0 and b0 in case 1).

As described above, the PUCCH resource other than PUCCH resource 1 (Ch1)to be implicitly signaled when the number of downlink component carriersis two (FIG. 28C) (i.e., PUCCH resource 3 (Ch3) herein) is set as thePUCCH resource to be implicitly signaled in case 6 (i.e., where thenumber of downlink component carriers is four). Accordingly, even whenthe number of downlink component carriers is four, the ACK/NACK mappingtable used when the number of downlink component carriers is two can beused to report the PUCCH resource by implicit signaling.

In this manner, in case 6, it is possible to prevent occurrence of thesituation where terminal 200 cannot identify the implicitly signaledPUCCH resource in PCell. More specifically, it is possible to preventunnecessary retransmission processing from occurring in base station 100due to the situation where terminal 200 cannot identify the position ofthe PUCCH resource used for feeding back the response signals.

Moreover, in case 6, a part of the PUCCH resources used for feeding backthe response signals is reported to terminal 200 from base station 100by implicit signaling. Accordingly, as compared with a case where basestation 100 reports all the PUCCH resources to terminals 200 by explicitsignaling, the number of PUCCH resources to be explicitly signaled canbe reduced, which in turn reduces an increase in the overhead of PUCCH.

It should be noted that, the ACK/NACK mapping table is by no meanslimited to the one illustrated in FIG. 32A, and the ACK/NACK mappingtables illustrated in FIG. 32B and FIG. 32C can be used, for example.

In FIG. 32B, the bit representing the result of error detection on theCW received in PCell is “b1.” In FIG. 32B, the PUCCH resource to beimplicitly signaled is PUCCH resource 2 (Ch2). As illustrated in FIG.32B, when PUCCH resource 2 (Ch2) is used, bit b1 is always an “ACK.”Accordingly, PUCCH resource 2 (Ch2) is the PUCCH resource used only whenterminal 200 succeeds in receiving the PDCCH intended for terminal 200in PCell (b1=ACK). More specifically, PUCCH resource 2 (Ch2) is not usedwhen terminal 200 fails to receive the PDCCH intended for terminal 200in PCell (b1=DTX). In other words, PUCCH resource 2 illustrated in FIG.32B supports implicit signaling for bit b1.

In addition, in comparison between FIG. 32B and case 1 (FIG. 28C), thecase in FIG. 32B and case 1 use the same number of ACK/NACK bits (i.e.,four bits) and the same ACK/NACK mapping table, but use a differentPUCCH resource to be implicitly signaled. In addition, the cases in FIG.32B and FIG. 28C include a different combination of the PUCCH resourceto be implicitly signaled and the bit representing the result of errordetection on the CW received in PCell (i.e., PUCCH resource 2 and b1 inFIG. 32B and PUCCH resource 0 and b0 in FIG. 28C).

Likewise, the bit representing the result of error detection on the CWreceived on PCell is “b2” in FIG. 32C. In addition, the PUCCH resourceto be implicitly signaled is PUCCH resource 2 (Ch2) in FIG. 32C. Asillustrated in FIG. 32C, when PUCCH resource 2 (Ch2) is used, bit b2 isalways an “ACK.” Accordingly, PUCCH resource 2 (Ch2) is the PUCCHresource used only when terminal 200 succeeds in receiving the PDCCHintended for terminal 200 in PCell (b2=ACK). More specifically, PUCCHresource 2 (Ch2) is not used when terminal 200 fails to receive thePDCCH intended for terminal 200 in PCell (b2=DTX). In other words, PUCCHresource 2 illustrated in FIG. 32C supports implicit signaling for bitb2.

In addition, in comparison between FIG. 32C and FIG. 28C (e.g., case 1),the case in FIG. 32C and case 1 use the same number of ACK/NACK bits(i.e., four bits) and the same ACK/NACK mapping table, but use adifferent PUCCH resource to be implicitly signaled.

Furthermore, in comparison between FIG. 32C and FIG. 28C (e.g., case 1),while the bits representing the results of error detection on the PDSCHin PCell 1 are “b0 and b1” in FIG. 28C, the bit representing the resultof error detection on the PDSCH in PCell is “b2” in FIG. 32C. Morespecifically, the bits representing the results of error detection onthe PDSCH in PCell are different in FIG. 32C and FIG. 28C. Moreover, thecases in FIG. 32C and FIG. 28C use a different combination of the PUCCHresource to be implicitly signaled and the bit representing the resultof error detection on the CW received in PCell (i.e., PUCCH resource 2and b2 in FIG. 32C and PUCCH resource 0 and b0 in FIG. 28C).

(Case 7: Where Number of Downlink Component Carriers is Three, Number ofACK/NACK Bit is Four and Non-MIMO Mode is Configured in TransmissionMode of PCell)

More specifically, the non-MIMO mode is configured in PCell and thenon-MIMO mode is configured in one of SCells 1 and 2 while the MIMO modeis configured in the other one of SCells 1 and 2 in case 7.

FIG. 33 illustrates the method of determining the PUCCH resource inPCell and SCells 1 and 2 in the case where the number of downlinkcomponent carriers is three, for example.

In case 7, terminals 200 use mapping for four bits (i.e., ACK/NACKmapping table) illustrated in FIG. 27C and FIG. 28C. As illustrated inFIG. 34A (i.e., the same ACK/NACK mapping table as that in FIG. 28C),bit b0 represents the result of error detection on single CW received inPCell and bits b1 to b3 represent the results of error detection onthree CWs received in SCells 1 and 2.

In addition, in case 7, the PUCCH resources for the maximum number ofCWs supported in PCell in dynamic scheduling are implicitly signaled.Accordingly, since the non-MIMO mode is configured in PCell in case 7,one PUCCH resource is implicitly signaled.

In case 7, the PUCCH resource to be implicitly signaled is PUCCHresource 3 (Ch3) as illustrated in FIG. 34A. In other words, the PUCCHresources to be explicitly signaled are PUCCH resources 1, 2 and 4 (Chs1, 2 and 4) in FIG. 34A.

As illustrated in FIG. 34A, when PUCCH resource 3 (Ch3) is used, bit b0is always an “ACK” as in case 6. More specifically, the ratio of ACK toNACK for PUCCH resource 3 (Ch3) as illustrated in FIG. 34A (A:N) isA:N=1:0(=4:0). In other words, terminal 200 uses PUCCH resource 3 (Ch3)for transmission of the response signals only when the result of errordetection on the CW received in PCell is an “ACK” (b0=ACK). To put itdifferently, when terminal 200 fails to receive the PDCCH intended forterminal 200 in PCell (b0=DTX), PUCCH resource 3 (Ch3) is not used. Inshort, PUCCH resource 3 (Ch3) supports implicit signaling for bit b0.

Accordingly, it is possible to prevent unnecessary retransmissionprocessing from occurring in base station 100 due to the situation whereterminal 200 cannot identify the position of the PUCCH resource used fortransmission of the response signals.

As described above, in the ACK/NACK mapping table (FIG. 34A) in case 6,the PUCCH resource associated in a one-to-one correspondence with thetop CCE index of the CCEs occupied by the PDCCH indicating theassignment of PDSCH in PCell (i.e., PUCCH resource 3 in FIG. 34A) is thePUCCH resource in which the result of error detection on the CW receivedin PCell becomes only an ACK in each of the error detection resultpatterns associated with the PUCCH resource (i.e., b0 in FIG. 34A).

Alternatively, in the ACK/NACK mapping table in case 7, the PUCCHresource to be implicitly signaled may be the PUCCH resource in whichthe result of error detection on the CW received in PCell becomes only aNACK (i.e., result other than DTX) in each of the error detection resultpatterns associated with the PUCCH resource.

For example, case 7 is compared with case 1 (the number of downlinkcomponent carriers is two and the number of ACK/NACK bits is four). Incase 1 (FIG. 28C), the PUCCH resource to be implicitly signaled is PUCCHresource 1 (Ch1). In contrast to case 1, the PUCCH resource to beimplicitly signaled is PUCCH resource 3 (Ch3) in case 7 (FIG. 34A). Inother words, case 7 (PCell: non-MIMO mode) and case 1 (PCell: MIMO mode)use the same number of ACK/NACK bits and the same ACK/NACK mappingtable, but use a different PUCCH resource to be implicitly signaled.

In addition, case 7 and case 1 include a different combination of thePUCCH resource to be implicitly signaled and the bit representing theresult of error detection on the CW received in PCell (i.e., PUCCHresource 3 and b0 in case 7 and PUCCH resource 0 and b0 in case 1).

As described above, the PUCCH resource other than PUCCH resource 1 (Ch1)to be implicitly signaled when the number of downlink component carriersis two (FIG. 28C) (i.e., PUCCH resource 3 (Ch3) herein) is set as thePUCCH resource to be implicitly signaled in case 7 (i.e., the number ofdownlink component carriers is three (FIG. 34A)). Accordingly, even whenthe number of downlink component carriers is three, the ACK/NACK mappingtable used when the number of downlink component carriers is two can beused to report the PUCCH resource by implicit signaling.

In this manner, in case 7, it is possible to prevent occurrence of thesituation where terminal 200 cannot identify the implicitly signaledPUCCH resource in PCell. To put it more specifically, it is possible toprevent unnecessary retransmission processing from occurring in basestation 100 due to the situation where terminal 200 cannot identify theposition of the PUCCH resource used for transmission of the responsesignals.

Moreover, in case 7, a part of the PUCCH resources used for feeding backthe response signals is reported to terminal 200 from base station 100by implicit signaling. Accordingly, as compared with a case where basestation 100 reports all the PUCCH resources to terminals 200 by explicitsignaling, the number of PUCCH resources to be explicitly signaled canbe reduced, which in turn reduces an increase in the overhead of PUCCH.

It should be noted that, the ACK/NACK mapping table is by no meanslimited to the one illustrated in FIG. 34A, and the ACK/NACK mappingtables illustrated in FIG. 34B and FIG. 34C can be used, for example.

In FIG. 34B, the bit representing the result of error detection on theCW received in PCell is “b1.” In FIG. 34B, the PUCCH resource to beimplicitly signaled is PUCCH resource 2 (Ch2). As illustrated in FIG.34B, when PUCCH resource 2 (Ch2) is used, bit b1 is always an “ACK.”Accordingly, PUCCH resource 2 (Ch2) is the PUCCH resource used only whenterminal 200 succeeds in receiving the PDCCH intended for terminal 200in PCell (b1=ACK). In other words, PUCCH resource 2 (Ch2) is not usedwhen terminal 200 fails to receive the PDCCH intended for terminal 200in PCell (b1=DTX). In short, PUCCH resource 2 illustrated in FIG. 34Bsupports implicit signaling for bit b1.

In addition, in comparison between FIG. 34B and case 1 (FIG. 28C), thecase in FIG. 32B and case 1 use the same number of ACK/NACK bits (i.e.,four bits) and the same ACK/NACK mapping table, but a different PUCCHresource to be implicitly signaled. In addition, the cases in FIG. 34Band FIG. 28C include a different combination of the PUCCH resource to beimplicitly signaled and the bit representing the result of errordetection on the CW received in PCell (i.e., PUCCH resource 2 and b1 inFIG. 34B and PUCCH resource 0 and b0 in FIG. 28C).

Likewise, the bit representing the result of error detection on the CWreceived on PCell is “b2” in FIG. 34C. In addition, the PUCCH resourceto be implicitly signaled is PUCCH resource 2 (Ch2) in FIG. 34C. Asillustrated in FIG. 34C, when PUCCH resource 2 (Ch2) is used, bit b2 isalways an “ACK.” Accordingly, PUCCH resource 2 (Ch2) is the PUCCHresource used only when terminal 200 succeeds in receiving the PDCCHintended for terminal 200 in PCell (b2=ACK). In other words, PUCCHresource 2 (Ch2) is not used when terminal 200 fails to receive thePDCCH intended for terminal 200 in PCell (b2=DTX). In short, PUCCHresource 2 illustrated in FIG. 34C supports implicit signaling for bitb2.

In addition, in comparison between FIG. 34C and case 1 (FIG. 28C), thecase in FIG. 34C and case 1 use the same number of ACK/NACK bits (i.e.,four bits) and the same ACK/NACK mapping table, but a different PUCCHresource to be implicitly signaled.

Furthermore, in comparison between FIG. 34C and case 1 (FIG. 28C), whilethe bits representing the results of error detection on the PDSCH inPCell 1 are “b0 and b1” in FIG. 28C, the bit representing the result oferror detection on the PDSCH in PCell is “b2” in FIG. 34C. Morespecifically, the bits representing the results of error detection onthe PDSCH in PCell are different in FIG. 34C and FIG. 28C. Moreover, thecases in FIG. 34C and FIG. 28C include a different combination of thePUCCH resource to be implicitly signaled and the bit representing theresult of error detection on the CW received in PCell (i.e., PUCCHresource 2 and b2 in FIG. 34C and PUCCH resource 0 and b0 in FIG. 28C).

(Case 8: Where Number of Downlink Component Carriers is Three and Numberof ACK/NACK Bits is Three)

More specifically, the non-MIMO mode is configured in each of PCell andSCells 1 and 2 in case 8.

FIG. 35 illustrates the method of determining the PUCCH resource inPCell and SCells 1 and 2 when the number of downlink component carriersis three, for example.

In case 8, terminals 200 use mapping for three bits (i.e., ACK/NACKmapping table) illustrated in FIG. 27B and FIG. 28B. As illustrated inFIG. 36A (i.e., the same ACK/NACK mapping table as that in FIG. 28B),bit b2 represents the result of error detection on single CW received inPCell and bits b0 and b1 represent the results of error detection on twoCWs received in SCells 1 and 2, respectively.

In addition, in case 8, the PUCCH resources for the maximum number ofCWs supported in PCell in dynamic scheduling are implicitly signaled.Accordingly, since the non-MIMO mode is configured in PCell in case 8,one PUCCH resource is implicitly signaled.

In case 8, the PUCCH resource to be implicitly signaled is PUCCHresource 3 (Ch3) as illustrated in FIG. 36A. More specifically, thePUCCH resource to be explicitly signaled is PUCCH resources 1 and 2 (Chs1 and 2) in FIG. 36A.

As illustrated in FIG. 36A, when PUCCH resource 3 (Ch3) is used, bit b2is always an “ACK” as in cases 6 and 7. More specifically, the ratio ofACK to NACK for PUCCH resource 3 (Ch3) as illustrated in FIG. 34A (A:N)is A:N=1:0(=3:0). In other words, terminal 200 uses PUCCH resource 3(Ch3) for transmission of the response signals only when the result oferror detection on the CW received in PCell is an “ACK” (b2=ACK). To putit differently, when terminal 200 fails to receive the PDCCH intendedfor terminal 200 in PCell (b2=DTX), PUCCH resource 3 (Ch3) is not used.In short, PUCCH resource 3 (Ch3) supports implicit signaling for bit b2.

Accordingly, it is possible to prevent unnecessary retransmissionprocessing from occurring due to a situation where terminal 200 cannotidentify the position of the PUCCH resource used for transmission of theresponse signals.

As described above, in the ACK/NACK mapping table (FIG. 36A) in case 8,the PUCCH resource associated in a one-to-one correspondence with thetop CCE index of the CCEs occupied by the PDCCH indicating theassignment of PDSCH in PCell (i.e., PUCCH resource 3 in FIG. 36A) is thePUCCH resource in which the result of error detection on the CW receivedin PCell becomes only an ACK in each of the error detection resultpatterns associated with the PUCCH resource (i.e., b2 in FIG. 36A).

Alternatively, in the ACK/NACK mapping table in case 8, the PUCCHresource to be implicitly signaled may be the PUCCH resource in whichthe result of error detection on the CW received in PCell becomes only aNACK (i.e., result other than DTX) in each of the error detection resultpatterns associated with the PUCCH resource.

In addition, case 8 is compared with case 2 (the number of downlinkcomponent carriers is two while the number of ACK/NACK bits is three andthe MIMO mode is configured in PCell), for example. In case 2 (FIG.28B), the PUCCH resource to be implicitly signaled is PUCCH resource 1(Ch1). In contrast to case 2, the PUCCH resource to be implicitlysignaled is PUCCH resource 3 (Ch3) in case 8 (FIG. 36A). In other words,case 8 (PCell: non-MIMO mode) and case 2 (PCell: MIMO mode) use the samenumber of ACK/NACK bits and the same ACK/NACK mapping table, but adifferent PUCCH resource to be implicitly signaled.

Furthermore, while the bits representing the results of error detectionon the PDSCH in PCell 1 are “b0 and b1” in FIG. 28B (i.e., case 2), thebit representing the result of error detection on the PDSCH in PCell is“b2” in FIG. 36A. More specifically, the bits representing the resultsof error detection on the PDSCH in PCell are different in FIG. 34A andFIG. 28B. Moreover, case 8 and case 1 include a different combination ofthe PUCCH resource to be implicitly signaled and the bit representingthe result of error detection on the CW received in PCell (i.e., PUCCHresource 3 and b2 in case 8 and PUCCH resource 0 and b0 in case 1).

As described above, in case 8 (i.e., when the number of downlinkcomponent carriers is three (FIG. 36A)), the PUCCH resource other thanthe PUCCH resource 1 (Ch1) to be implicitly signaled when the number ofdownlink component carriers is two (FIG. 28B) (i.e., PUCCH resource 3(Ch3) herein) is set as the PUCCH resource to be implicitly signaled.Accordingly, even when the number of downlink component carriers isthree, the ACK/NACK mapping table used when the number of downlinkcomponent carriers is two can be used to report the PUCCH resource byimplicit signaling.

In this manner, in case 8, it is possible to prevent occurrence of thesituation where terminal 200 cannot identify the implicitly signaledPUCCH resource in PCell. In other words, it is possible to preventunnecessary retransmission processing from occurring in base station 100due to a situation where terminal 200 cannot identify the position ofthe PUCCH resource used for feeding back the response signals.

Moreover, in case 8, a part of the PUCCH resources used for feeding backthe response signals is reported to terminal 200 from base station 100by implicit signaling. Accordingly, as compared with a case where basestation 100 reports all the PUCCH resources to terminals 200 by explicitsignaling, the number of PUCCH resources to be explicitly signaled canbe reduced, which in turn reduces an increase in the overhead of PUCCHin case 8.

It should be noted that, the ACK/NACK mapping table is by no meanslimited to the one illustrated in FIG. 36A, and the ACK/NACK mappingtable illustrated in FIG. 36B can be used, for example.

In FIG. 36B, the bit representing the result of error detection on theCW received in PCell is “b2.” In FIG. 36B, the PUCCH resource to beimplicitly signaled is PUCCH resource 2 (Ch2). As illustrated in FIG.36B, when PUCCH resource 2 (Ch2) is used, bit b2 is always an “ACK.”Accordingly, PUCCH resource 2 (Ch2) is the PUCCH resource used only whenterminal 200 succeeds in receiving the PDCCH intended for terminal 200in PCell (b2=ACK). In other words, PUCCH resource 2 (Ch2) is not usedwhen terminal 200 fails to receive the PDCCH intended for terminal 200in PCell (b2=DTX). In short, PUCCH resource 2 illustrated in FIG. 36Bsupports implicit signaling for bit b2. More specifically, the bitsrepresenting the results of error detection on the PDSCH in PCell aredifferent in FIG. 36B and FIG. 28B. Moreover, the cases in FIG. 36B andFIG. 28C include a different combination of the PUCCH resource to beimplicitly signaled and the bit representing the result of errordetection on the CW received in PCell (i.e., PUCCH resource 2 and b2 inFIG. 36B and PUCCH resource 0 and b0 in FIG. 28B).

Hereinabove, a description has been provided regarding cases 1 to 8 ineach of which a different number of downlink component carriers and adifferent number of ACK/NACK bits are configured and a differenttransmission mode is configured in PCell.

As described above, terminal 200 (e.g., control sections 208) switchesthe combination of the PUCCH resource associated in a one-to-onecorrespondence with the top CCE index of the CCEs occupied by the PDCCHindicating the assignment of PDSCH in PCell (i.e., PUCCH resource to beimplicitly signaled) and the ACK/NACK bit representing the result oferror detection on PDSCH in PCell on the basis of the transmission modeconfigured in PCell. For example, terminal 200 switches the PUCCHresource to be implicitly signaled on the basis of the transmission modeconfigured in PCell. Alternatively, terminal 200 switches the ACK/NACKbit representing the result of error detection on PDSCH in PCell on thebasis of the transmission mode configured in PCell.

More specifically, terminal 200 uses different mapping for responsesignals between the case where the number of downlink component carriersis three or four while the number of ACK/NACK bits is equal to orgreater than the number of downlink component carriers but not greaterthan four and the non-MIMO mode is configured in PCell (e.g., cases 6 to8), and the case where the number of downlink component carriers is two(e.g., cases 1 to 4) or the case where the MIMO mode is configured inPCell (e.g., cases 1, 2 and 5).

For example, terminal 200 uses the ACK/NACK mapping table illustrated inFIG. 32, FIG. 34 or FIG. 36 in cases 6 to 8. Accordingly, even when aDTX occurs in PCell in which the non-MIMO mode is configured (i.e., whenthe PUCCH resource to be implicitly signaled cannot be identified),terminal 200 can identify the PUCCH resource to be used for feeding backthe response signals as described above (explicit signaling). In otherwords, in cases 6 to 8, the PUCCH resource can be reported by implicitsignaling without causing unnecessary retransmission processing in basestations 100. In addition, in cases 6 to 8, the overhead of PUCCH can bereduced by using implicit signaling as compared with the case where allthe PUCCH resources are reported by explicit signaling.

Meanwhile, in cases 1 to 5, terminals 200 use the ACK/NACK mapping tableillustrated in FIGS. 28A to C, for example. In FIGS. 28A to C, LTEfallback from two CCs is supported as in the case of Embodiment 1. Forexample, LTE fallback is supported in FIG. 28A because A/D is mapped tothe phase point (−1, 0) of PUCCH resource 1 and N/D is mapped to thephase point (1, 0) of PUCCH resource 1 when PCell performs single-CWprocessing and SCell also performs single-CW processing. Likewise, LTEfallback is supported in FIG. 28B because D/D/A is mapped to the phasepoint (−1, 0) of PUCCH resource 3 and D/D/N is mapped to the phase point(1, 0) of PUCCH resource 3 when PCell performs single-CW processing andSCell performs two-CW processing. In addition, LTE fallback is supportedin FIG. 28B because A/A/D is mapped to the phase point (−1, 0) of PUCCHresource 1 and A/N/D is mapped to the phase point (0, 1) of PUCCHresource 1 while N/A/D is mapped to the phase point (0, −1) of PUCCHresource 1 and N/N/D is mapped to the phase point (1, 0) of PUCCHresource 1 when PCell performs two-CW processing and SCell performssingle-CW processing. Likewise, LTE fallback is supported in FIG. 28Cbecause A/A/D/D is mapped to the phase point (−1, 0) of PUCCH resource 1and A/N/D/D is mapped to the phase point (0, 1) of PUCCH resource 1while N/A/D/D is mapped to the phase point (0, −1) of PUCCH resource 1and N/N/D/D is mapped to the phase point (1, 0) of PUCCH resource 1. Inshort, FIGS. 28A to C correspond to the mapping that supports mappingfor response signals when the number of CCs is one (e.g., FIGS. 6A andB). In this manner, the response signals for PCell and SCell can becorrectly determined even when the understanding about the number of CCsconfigured for the terminal is different between base station 100 andterminal 200.

It should be noted that, LTE fallback is not supported in the ACK/NACKmapping tables used in cases 6 to 8 and illustrated in FIG. 32, FIG. 34and FIG. 36. However, the possibility of the configuration of terminal200 being changed from the situation where the ACK/NACK mapping tablesused in cases 6 to 8 and illustrated in FIG. 32, FIG. 34 and FIG. 36(i.e., the number of downlink component carriers: three or four) to thesituation where LTE fallback is required is very low. Accordingly, evenwhen terminal 200 uses the ACK/NACK mapping tables illustrated in FIG.32, FIG. 34 and FIG. 36 in cases 6 to 8, it is unlikely that use of theACK/NACK mapping tables affects the LTE fallback.

Moreover, as illustrated in FIG. 28B and FIG. 36 or FIG. 28C, FIG. 32and FIG. 34, the associations among the patterns of results of errordetection (i.e., b0 to b3), PUCCH resources (CH1 to CH4), and the phasepoints in each of the PUCCH resources are the same. To put itdifferently, regardless of whether the transmission mode of PCell is theMIMO mode or the non-MIMO mode, base station 100 and terminals 200 usethe same ACK/NACK mapping table according to the number of ACK/NACKbits. More specifically, base station 100 and terminals 200 can reusethe ACK/NACK mapping table (FIGS. 28B and C) optimized for the casewhere the number of downlink component carriers is two, although thePUCCH resource to be implicitly signaled is switched in comparisonbetween a case where two downlink component carriers are configured andin a case where three or four downlink component carriers areconfigured.

It should be noted that, the ACK/NACK mapping tables illustrated in FIG.32, FIG. 34 and FIG. 36 represent the mapping in which the number ofPUCCH resources each allowing the ACK/NACK to be determined only bydetermining the PUCCH resource in which response signals are reported issmoothed out among the bits forming an error detection result pattern inEmbodiment 2 as in the case of Embodiment 1. More specifically, basestation 100 determines the ACK/NACK using the mapping that smooths out,among the bits, the number of PUCCH resources each allowing the ACK/NACKto be determined only by determining the PUCCH resource in which theresponse signals are reported. To put it differently, the differencebetween the maximum and minimum values of the number of PUCCH resourcesthat results in A:N=1:0 (or A:N=0:1) is not greater than one for theresults of error detection that form an error detection result patternin FIG. 32, FIG. 34 and FIG. 36. In this case, the PUCCH resourceresulting in A:N=1:0 (or A:N=0:1) for a certain pattern for results oferror detection is the PUCCH resource that results in only an ACK (orNACK) as the result of error detection indicated at all the phase pointsin the PUCCH resource. Accordingly, it is possible to improve thecharacteristics of response signals having poor transmissioncharacteristics as in Embodiment 1. To put it differently, it ispossible to obtain the same effects as those of Embodiment 1 by usingthe ACK/NACK mapping tables illustrated in FIG. 32, FIG. 34 and FIG. 36without switching the PUCCH resource to be implicitly signaled.

Embodiments 1 and 2 of the claimed invention have been described above.

In the above described embodiments, ZAC sequences, Walsh sequences, andDFT sequences are described as examples of the sequences used forspreading. However, instead of ZAC sequences, sequences that can beseparated using different cyclic shift values, other than ZAC sequencesmay be used. For example, the following sequences may be used forprimary-spreading: generalized chirp like (GCL) sequences; constantamplitude zero auto correlation (CAZAC) sequences; zadoff-chu (ZC)sequences; PN sequences such as M sequences or orthogonal Gold codesequences; or sequences having a steep autocorrelation characteristic onthe time axis randomly generated by computer. In addition, instead ofWalsh sequences and DFT sequences, any sequences may be used asorthogonal code sequences as long as the sequences are mutuallyorthogonal or considered to be substantially orthogonal to each other.In the abovementioned description, the resource of response signals(e.g., A/N resource and bundled ACK/NACK resource) is defined by thefrequency position, cyclic shift value of the ZAC sequence and sequencenumber of the orthogonal code sequence.

Moreover, control section 101 of base station 100 is configured tocontrol mapping in such a way that downlink data and the downlinkassignment control information for the downlink data are mapped to thesame downlink component carrier in the embodiments described above, butis by no means limited to this configuration. To put it differently,even if downlink data and the downlink assignment control informationfor the downlink data are mapped to different downlink componentcarriers, the technique described in each of the embodiments can beapplied as long as the correspondence between the downlink assignmentcontrol information and the downlink data is clear.

Furthermore, as the processing sequence in terminals, the case whereIFFT transform is performed after the primary-spreading andsecondary-spreading has been described. However, the processing sequencein terminals is by no means limited to this sequence. As long as IFFTprocessing is performed after the primary-spreading processing, anequivalent result can be obtained regardless of the position of thesecondary-spreading processing.

In each of the embodiments, the description has been provided withantennas, but the claimed invention can be applied to antenna ports inthe same manner.

The term “antenna port” refers to a logical antenna including one ormore physical antennas. In other words, the term “antenna port” does notnecessarily refer to a single physical antenna, and may sometimes referto an antenna array including a plurality of antennas, and/or the like.

For example, 3GPP LTE does not specify the number of physical antennasforming an antenna port, but specifies an antenna port as a minimum unitallowing base stations to transmit different reference signals.

In addition, an antenna port may be specified as a minimum unit to bemultiplied by a precoding vector weighting.

The above-noted embodiments have been described by examples of hardwareimplementations, but the claimed invention can be also implemented bysoftware in conjunction with hardware.

In addition, the functional blocks used in the descriptions of theembodiments are typically implemented as LSI devices, which areintegrated circuits. The functional blocks may be formed as individualchips, or a part or all of the functional blocks may be integrated intoa single chip. The term “LSI” is used herein, but the terms “IC,”“system LSI,” “super LSI” or “ultra LSI” may be used as well dependingon the level of integration.

In addition, the circuit integration is not limited to LSI and may beachieved by dedicated circuitry or a general-purpose processor otherthan an LSI. After fabrication of LSI, a field programmable gate array(FPGA), which is programmable, or a reconfigurable processor whichallows reconfiguration of connections and settings of circuit cells inLSI may be used.

Should a circuit integration technology replacing LSI appear as a resultof advancements in semiconductor technology or other technologiesderived from the technology, the functional blocks could be integratedusing such a technology. Another possibility is the application ofbiotechnology and/or the like.

The disclosures of the specifications, the drawings, and the abstractsincluded in Japanese Patent Application No. 2010-208068, filed on Sep.16, 2010, Japanese Patent Application No. 2010-231866, filed on Oct. 14,2010 and Japanese Patent Application No. 2011-072045, filed on Mar. 29,2011 are incorporated herein by reference in their entirety.

INDUSTRIAL APPLICABILITY

The claimed invention can be applied to mobile communication systemsand/or the like.

REFERENCE SIGNS LIST

-   -   100 Base station    -   101, 208 Control section    -   102 Control information generating section    -   103 Coding section    -   104 Modulation section    -   105 Coding section    -   106 Data transmission controlling section    -   107 Modulation section    -   108 Mapping section    -   109, 218-1, 218-2, 218-3 IFFT section    -   110, 219-1, 219-2, 219-3 CP adding section    -   111, 222 Radio transmitting section    -   112, 201 Radio receiving section    -   113, 202 CP removing section    -   114 PUCCH extracting section    -   115 Despreading section    -   116 Sequence controlling section    -   117 Correlation processing section    -   118 A/N determining section    -   119 Bundled A/N despreading section    -   120 IDFT section    -   121 Bundled A/N determining section    -   122 Retransmission control signal generating section    -   200 Terminal    -   203 FFT section    -   204 Extraction section    -   205, Demodulation section    -   206, 210 Decoding section    -   207 Determination section    -   211 CRC section    -   212 Response signal generating section    -   213 Coding and modulation section    -   214-1, 214-2 Primary-spreading section    -   215-1, 215-2 Secondary-spreading section    -   216 DFT section    -   217 Spreading section    -   220 Time-multiplexing section    -   221 Selection section

The invention claimed is:
 1. A communication apparatus comprising: areceiver which, in operation, receives downlink data on a firstcomponent carrier and a second component carrier; and a transmitterwhich, in operation, transmits a block of ACK/NACK bits that indicateserror detection results of the downlink data on the first componentcarrier and the second component carrier, wherein the block of ACK/NACKbits is mapped, according to a mapping table, to a phase point amongphase points on an uplink control channel resource (PUCCH resource)selected from a plurality of PUCCH resources, wherein the mapping ruledefines: a first number of PUCCH resource(s) respectively associatedwith set(s) of phase points, wherein all phase points in the set aremapped with acknowledgment (ACK) or all phase points in the set aremapped with negative acknowledgement (NACK)/discontinuous transmission(DTX) in one of the error detection results; a second number of PUCCHresource(s) respectively associated with set(s) of phase points, whereinall phase points in the set are mapped with ACK or all phase points inthe set are mapped with NACK/DTX in another one of the error detectionresults; and a maximum difference between the first number of PUCCHresources and the second number of PUCCH resource(s) is one or zero;wherein the receiver receives the downlink data in a retransmission whenthe retransmission is indicated by the transmitted block of ACK/NACKbits.
 2. The communication apparatus according to claim 1, wherein theplurality of PUCCH resources include a first PUCCH resource and a secondPUCCH resource, the first PUCCH resource corresponds to a first ControlChannel Elements (CCE) index of a plurality of CCEs which are used totransmit downlink control information, and the second PUCCH resourcecorresponds to a number obtained by adding one to the first CCE index.3. The communication apparatus according to claim 1, wherein of thefirst component carrier and the second component carrier, only the firstcomponent carrier is paired with an uplink component carrier used totransmit the block of ACK/NACK bits.
 4. The communication apparatusaccording to claim 1, wherein the mapping rule defines: on the PUCCHresource for which all phase points in the set are mapped with DTX ofthe second component carrier: ACK of the first component carrier ismapped to a phase point (−1, 0) and NACK of the first component carrieris mapped to a phase point (1, 0); or ACK/ACK of the first componentcarrier is mapped to a phase point (−1, 0), ACK/NACK of the firstcomponent carrier is mapped to a phase point (0, 1), NACK/ACK of thefirst component carrier is mapped to a phase point (0, −1), andNACK/NACK of the first component carrier is mapped to a phase point (1,0).
 5. The communication apparatus according to claim 1, wherein anumber of error detection results of the downlink data on the firstcomponent carrier and a number of error detection results of thedownlink data on the second component carrier are one and two or two andone; and the mapping rule defines: on the PUCCH resource for which allphase points in the set are mapped with DTX of the second componentcarrier: ACK of the first component carrier is mapped to a phase point(−1, 0) and NACK of the first component carrier is mapped to a phasepoint (1, 0); or ACK/ACK of the first component carrier is mapped to aphase point (−1, 0), ACK/NACK of the first component carrier is mappedto a phase point (0, 1), NACK/ACK of the first component carrier ismapped to a phase point (0, −1), and NACK/NACK of the first componentcarrier is mapped to a phase point (1, 0).
 6. The communicationapparatus according to claim 1, wherein a number of the plurality ofPUCCH resources is three and a number of the error detection results isthree; in one of the three PUCCH resources, two of the three errordetection results have all phase points in the set mapped with ACK orall phase points in the set mapped with NACK/DTX; and in two of thethree PUCCH resources, one of the three error detection results has allphase points in the set mapped with ACK or all phase points in the setmapped with NACK/DTX.
 7. The communication apparatus according to claim1, wherein a number of the plurality of PUCCH resources is four and anumber of the error detection results is four; in two of the four PUCCHresources, two of the four error detection results have all phase pointsin the set mapped with ACK or all phase points in the set mapped withNACK/DTX; and in two of the four PUCCH resources, one of the four errordetection results has all phase points in the set mapped with ACK or allphase points in the set mapped with NACK/DTX.
 8. A communication methodcomprising: receiving downlink data on a first component carrier and asecond component carrier; transmitting a block of ACK/NACK bits thatindicates error detection results of the downlink data on the firstcomponent carrier and the second component carrier, wherein the block ofACK/NACK bits is mapped, according to a mapping table, to a phase pointamong phase points on an uplink control channel resource (PUCCHresource) selected from a plurality of PUCCH resources, wherein themapping rule defines: a first number of PUCCH resource(s) respectivelyassociated with set(s) of phase points, wherein all phase points in theset are mapped with acknowledgment (ACK) or all phase points in the setare mapped with negative acknowledgement (NACK)/discontinuoustransmission (DTX) in one of the error detection results; a secondnumber of PUCCH resource(s) respectively associated with set(s) of phasepoints, wherein all phase points in the set are mapped with ACK or allphase points in the set are mapped with NACK/DTX in another one of theerror detection results; and a maximum difference between the firstnumber of PUCCH resources and the second number of PUCCH resource(s) isone or zero; and receiving the downlink data in a retransmission whenthe retransmission is indicated by the transmitted block of ACK/NACKbits.
 9. The communication method according to claim 8, wherein theplurality of PUCCH resources include a first PUCCH resource and a secondPUCCH resource, the first PUCCH resource corresponds to a first ControlChannel Elements (CCE) index of a plurality of CCEs which are used totransmit downlink control information, and the second PUCCH resourcecorresponds to a number obtained by adding one to the first CCE index.10. The communication method according to claim 8, wherein of the firstcomponent carrier and the second component carrier, only the firstcomponent carrier is paired with an uplink component carrier used totransmit the block of ACK/NACK bits.
 11. The communication methodaccording to claim 8, wherein the mapping rule defines: on the PUCCHresource for which all phase points in the set are mapped with DTX ofthe second component carrier: ACK of the first component carrier ismapped to a phase point (−1, 0) and NACK of the first component carrieris mapped to a phase point (1, 0); or ACK/ACK of the first componentcarrier is mapped to a phase point (−1, 0), ACK/NACK of the firstcomponent carrier is mapped to a phase point (0, 1), NACK/ACK of thefirst component carrier is mapped to a phase point (0, −1), andNACK/NACK of the first component carrier is mapped to a phase point (1,0).
 12. The communication method according to claim 8, wherein a numberof error detection results of the downlink data on the first componentcarrier and a number of error detection results of the downlink data onthe second component carrier are one and two or two and one; and themapping rule defines: on the PUCCH resource for which all phase pointsin the set are mapped with DTX of the second component carrier: ACK ofthe first component carrier is mapped to a phase point (−1, 0) and NACKof the first component carrier is mapped to a phase point (1, 0); orACK/ACK of the first component carrier is mapped to a phase point (−1,0), ACK/NACK of the first component carrier is mapped to a phase point(0, 1), NACK/ACK of the first component carrier is mapped to a phasepoint (0, −1), and NACK/NACK of the first component carrier is mapped toa phase point (1, 0).
 13. The communication method according to claim 8,wherein a number of the plurality of PUCCH resources is three and anumber of the error detection results is three; in one of the threePUCCH resources, two of the three error detection results have all phasepoints in the set mapped with ACK or all phase points in the set mappedwith NACK/DTX; and in two of the three PUCCH resources, one of the threeerror detection results has all phase points in the set mapped with ACKor all phase points in the set mapped with NACK/DTX.
 14. Thecommunication method according to claim 8, wherein a number of theplurality of PUCCH resources is four and a number of the error detectionresults is four; in two of the four PUCCH resources, two of the fourerror detection results have all phase points in the set mapped with ACKor all phase points in the set mapped with NACK/DTX; and in two of thefour PUCCH resources, one of the four error detection results has allphase points in the set mapped with ACK or all phase points in the setmapped with NACK/DTX.